Light emitting element with layers having complementary colors for absorbing light

ABSTRACT

A light emitting element with a high contrast is realized. A light emitting device with a high contrast is achieved by using the light emitting element with an excellent contrast. The light emitting element has a layer containing a light emitting substance interposed between a first electrode and a second electrode, and the layer containing the light emitting substance includes a light emitting layer, a layer containing a first organic compound, and a layer containing a second organic compound. The first electrode has a light-transmitting property, and the layer containing the first organic compound and the layer containing the second organic compound are interposed between the second electrode and the light emitting layer. Furthermore, color of the first organic compound and color of the second organic compound are complementary.

This application is a continuation of application Ser. No. 11/715,145filed on Mar. 7, 2007 (now U.S. Pat. No. 8,164,088 issued Apr. 24,2012).

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a current-excitation light emittingelement. In addition, the present invention relates to a light emittingdevice and an electronic device each having the light emitting element.

2. Description of the Related Art

In recent years, a light emitting element using a light emitting organiccompound has been actively researched and developed. A basic structureof this light emitting element is formed by interposing a layercontaining a light emitting organic compound between a pair ofelectrodes. By application of a voltage to this element, electrons andholes are separately injected from the pair of electrodes into the layercontaining a light emitting organic compound, and a current flows. Then,recombination of these carriers (the electrons and holes) causes thelight emitting organic compound to be in an excited state and to emitlight when the excited state returns to a ground state. Owing to such amechanism, the light emitting element as described above is referred toas a current-excitation light emitting element.

It is to be noted that an excited state formed by an organic compoundcan be a singlet excited state or a triplet excited state. Lightemission from the singlet excited state is referred to as fluorescence,and light emission from the triplet excited state is referred to asphosphorescence.

A great advantage of such a light emitting element is that the lightemitting element can be manufactured to be thin and lightweight becausethe light emitting element is formed of an organic thin film with athickness of, for example, approximately 0.1 μm. In addition, extremelyhigh response speed is another advantage, because time between carrierinjection and light emission is approximately 1 μsec or less. Thesecharacteristics are considered suitable for a flat panel displayelement.

Such a light emitting element is formed into a film shape. Thus, planeemission can be easily obtained by formation of a large-area element.This characteristic is hard to be obtained in a point light sourcetypified by an incandescent lamp or an LED, or a line light sourcetypified by a fluorescent lamp. Therefore, the above-described lightemitting element also has a high utility value as a plane light sourcewhich is applicable to lighting or the like.

For the light emitting element as described above, in general, at leastone of the pair of electrodes is formed using a light-transmittingmaterial and the other is formed using various materials. Light emissionfrom a light emitting substance passes through the electrode formedusing a light-transmitting material and is extracted to external.

However, when a material with high reflectivity is used for the otherelectrode (the electrode which is not formed using a light-transmittingmaterial), there has been a problem in that the electrode formed usingthe material with high reflectivity also reflects light from an externalsource, and thus, the contrast is decreased.

In order to solve the problem in that the contrast is decreased, astructure in which a polarizing element, a quarter-wave plate, or thelike is provided outside of the light emitting element has beenproposed.

However, the use of the polarizing element or the wave plate causesproblems such as changes in chromatic characteristics due to wavelengthdependence of the wave plate and view-angle dependence. Furthermore,provision of components such as the polarizing element and the waveplate increases the costs and complicates the manufacturing process,which has been a problem as well.

SUMMARY OF THE INVENTION

In view of the foregoing problem, it is an object of the presentinvention to provide a light emitting element which realizes a highcontrast. More specifically, it is an object of the present invention toprovide a light emitting element with a high contrast which can bemanufactured easily. Furthermore, it is another object of the presentinvention to provide a light emitting device which realizes a highcontrast by using the light emitting element excellent in contrast.

As a result of concerted study, the present inventors have found thatthe provision of a layer that absorbs visible light between a lightemitting layer and a second electrode, in a light emitting element thathas the light emitting layer interposed between a first electrode with alight-transmitting property and the second electrode, can achieve theobjects. The present inventors have also found that the presentinvention is particularly effective when the reflectivity of the secondelectrode is high.

In other words, one feature of a light emitting element of the presentinvention is to include a layer containing a light emitting substanceinterposed between a first electrode and a second electrode, where thelayer containing the light emitting substance includes a light emittinglayer, a layer containing a first organic compound, and a layercontaining a second organic compound; the first electrode has alight-transmitting property; the layer containing the first organiccompound and the layer containing the second organic compound areinterposed between the second electrode and the light emitting layer;and color of the first organic compound and color of the second organiccompound are complementary.

Another feature of the light emitting element of the present inventionis to include a layer containing a light emitting substance interposedbetween a first electrode and a second electrode, where the layercontaining the light emitting substance includes a light emitting layer,a layer containing a first organic compound, and a layer containing asecond organic compound; the first electrode has a light-transmittingproperty; the layer containing the first organic compound and the layercontaining the second organic compound are interposed between the secondelectrode and the light emitting layer; and the first organic compoundhas the absorption peak in a wavelength region of greater than or equalto 380 nm and less than 540 nm, and the second organic compound has theabsorption peak in a wavelength region of greater than or equal to 540nm and less than or equal to 760 nm.

Another feature of the light emitting element of the present inventionis to include a layer containing a light emitting substance interposedbetween a first electrode and a second electrode, where the layercontaining the light emitting substance includes a light emitting layer,a layer containing a first organic compound, and a layer containing asecond organic compound; the first electrode has a light-transmittingproperty; the layer containing the first organic compound and the layercontaining the second organic compound are interposed between the secondelectrode and the light emitting layer; the first organic compound isany of 3,4,9,10-perylenetetracarboxylic acid derivatives,1,4,5,8,-naphthalenetetracarboxylic acid derivatives, naphthacenederivatives, or nickel complexes; and the second organic compound is anyof phthalocyanine derivatives, pentacene derivatives,3,4,9,10-perylenetetracarboxylic-bis-benzimidazole derivatives, orviolanthrone derivatives.

In the above structure, it is preferable that a third layer containing aconductive material be provided between the layer containing the firstorganic compound and the layer containing the second organic compound.As the conductive material, indium tin oxide, indium tin oxidecontaining silicon or silicon oxide, indium zinc oxide, indium tin oxidecontaining tungsten oxide and zinc oxide, or the like is given.

In addition, in the above structure, it is preferable that a third layercontaining a semiconductor material be provided between the layercontaining the first organic compound and the layer containing thesecond organic compound. As the semiconductor material, titanium oxide,vanadium oxide, niobium oxide, molybdenum oxide, tungsten oxide, rheniumoxide, ruthenium oxide, cobalt oxide, nickel oxide, zinc oxide, copperoxide, tin oxide, zinc sulfide, gallium nitride, gallium aluminumnitride, or the like is given.

Another feature of the light emitting element of the present inventionis to include a layer containing a light emitting substance interposedbetween a first electrode and a second electrode, where the layercontaining the light emitting substance includes a light emitting layer,an N-type semiconductor layer and a P-type semiconductor layer; thefirst electrode, the light emitting layer, the N-type semiconductorlayer, the P-type semiconductor layer, and the second electrode areformed in this order; the first electrode has a light-transmittingproperty, and color of the N-type semiconductor layer and color of theP-type semiconductor layer are complementary.

Another feature of the light emitting element of the present inventionis to include a layer containing a light emitting substance interposedbetween a first electrode and a second electrode, where the layercontaining the light emitting substance includes a light emitting layer,an N-type semiconductor layer, and a P-type semiconductor layer; thefirst electrode, the light emitting layer, the N-type semiconductorlayer, the P-type semiconductor layer, and the second electrode areformed in this order; the first electrode has a light-transmittingproperty; and the N-type semiconductor layer has the absorption peak ina wavelength region of greater than or equal to 380 nm and less than 540nm, and the P-type semiconductor layer has the absorption peak in awavelength region of greater than or equal to 540 nm and less than orequal to 760 nm.

Another feature of the light emitting element of the present inventionis to include a layer containing a light emitting substance interposedbetween a first electrode and a second electrode, where the layercontaining the light emitting substance includes a light emitting layer,an N-type semiconductor layer, and a P-type semiconductor layer; thefirst electrode, the light emitting layer, the N-type semiconductorlayer, the P-type semiconductor layer, and the second electrode areformed in this order; the first electrode has a light-transmittingproperty; the N-type semiconductor layer contains any of3,4,9,10-perylenetetracarboxylicdianhydride,3,4,9,10-perylenetetracarboxylicdiimide,N,N′-dimethyl-3,4,9,10-perylenetetracarboxylicdiimide,1,4,5,8-naphthalenetetracarboxylicdianhydride, or1,4,5,8-naphthalenetetracarboxylicdiimide; and the P-type semiconductorlayer contains any of phthalocyanine, copper phthalocyanine, zincphthalocyanine, vanadyl phthalocyanine, titanyl phthalocyanine, nickelphthalocyanine, pentacene, or 6,13-diphenylpentacene.

Another feature of the light emitting element of the present inventionis to include a layer containing a light emitting substance interposedbetween a first electrode and a second electrode, where the layercontaining the light emitting substance includes a light emitting layer,an N-type semiconductor layer, and a P-type semiconductor layer; thefirst electrode, the light emitting layer, the N-type semiconductorlayer, the P-type semiconductor layer, and the second electrode areformed in this order; the first electrode has a light-transmittingproperty; and the N-type semiconductor layer has the absorption peak ina wavelength region of greater than or equal to 540 nm and less than orequal to 760 nm, and the P-type semiconductor layer has the absorptionpeak in a wavelength region of greater than or equal to 380 nm and lessthan 540 nm.

Another feature of the light emitting element of the present inventionis to include a layer containing a light emitting substance interposedbetween a first electrode and a second electrode, where the layercontaining the light emitting substance includes alight emitting layer,an N-type semiconductor layer, and a P-type semiconductor layer; thefirst electrode, the light emitting layer, the N-type semiconductorlayer, the P-type semiconductor layer, and the second electrode arefarmed in this order; the first electrode has a light-transmittingproperty; the N-type semiconductor layer contains any of(1,2,3,4,8,9,10,11,15,16,17,18,22,23,24,25-hexadecafluorophthalocyaninato)copper,(1,2,3,4,8,9,10,11,15,16,17,18,22,23,24,25-hexadecafluorophthalocyaninato)zinc,perfluoropentacene, or3,4,9,10-perylenetetracarboxylic-bis-benzimidazole; and the P-typesemiconductor layer contains any of naphthacene,5,12-diphenylnaphthacene, or rubrene.

Another feature of the light emitting element of the present inventionis to include a layer containing a light emitting substance interposedbetween a first electrode and a second electrode, where the layercontaining the light emitting substance includes a light emitting layer,a P-type semiconductor layer, and an N-type semiconductor layer; thefirst electrode, the light emitting layer, the P-type semiconductorlayer, the N-type semiconductor layer, and the second electrode areformed in this order; the first electrode has a light-transmittingproperty, and color of the P-type semiconductor layer and color of theN-type semiconductor layer are complementary.

Another feature of the light emitting element of the present inventionis to include a layer containing a light emitting substance interposedbetween a first electrode and a second electrode, where the layercontaining the light emitting substance includes a light emitting layer,a P-type semiconductor layer, and an N-type semiconductor layer; thefirst electrode, the light emitting layer, the P-type semiconductorlayer, the N-type semiconductor layer, and the second electrode areformed in this order; the first electrode has a light-transmittingproperty; and the P-type semiconductor layer has the absorption peak ina wavelength region of greater than or equal to 380 nm and less than 540nm, and the N-type semiconductor layer has the absorption peak-in awavelength region of greater than or equal to 540 nm and less than orequal to 760 nm.

Another feature of the light emitting element of the present inventionis to include a layer containing a light emitting substance interposedbetween a first electrode and a second electrode, where the layercontaining the light emitting substance includes a light emitting layer,a P-type semiconductor layer, and an N-type semiconductor layer; thefirst electrode, the light emitting layer, the P-type semiconductorlayer, the N-type semiconductor layer, and the second electrode areformed in this order; the first electrode has a light-transmittingproperty; the P-type semiconductor layer contains any of naphthacene,5,12-diphenylnaphthacene, or rubrene; and the N-type semiconductor layercontains any of(1,2,3,4,8,9,10,11,15,16,17,18,22,23,24,25-hexadecafluorophthalocyaninato)copper,(1,2,3,4,8,9,10,11,15,16,17,18,22,23,24,25-hexadecafluorophthalocyaninato)zinc,perfluoropentacene, or3,4,9,10-perylenetetracarboxylic-bis-benzimidazole.

Another feature of the light emitting element of the present inventionis to include a layer containing a light emitting substance interposedbetween a first electrode and a second electrode, where the layercontaining the light emitting substance includes a light emitting layer,a P-type semiconductor layer, and an N-type semiconductor layer; thefirst electrode, the light emitting layer, the P-type semiconductorlayer, the N-type semiconductor layer, and the second electrode areformed in this order; the first electrode has a light-transmittingproperty; and the P-type semiconductor layer has the absorption peak ina wavelength region of greater than or equal to 540 nm and less than orequal to 760 nm, and the N-type semiconductor layer has the absorptionpeak in a wavelength region of greater than or equal to 380 nm and lessthan 540 nm.

Another feature of the light emitting element of the present inventionis to include a layer containing a light emitting substance interposedbetween a first electrode and a second electrode, where the layercontaining the light emitting substance includes a light emitting layer,a P-type semiconductor layer, and an N-type semiconductor layer; thefirst electrode, the light emitting layer, the P-type semiconductorlayer, the N-type semiconductor layer, and the second electrode areformed in this order; the first electrode has a light-transmittingproperty; the P-type semiconductor layer contains any of phthalocyanine,copper phthalocyanine, zinc phthalocyanine, vanadyl phthalocyanine,titanyl phthalocyanine, nickel phthalocyanine, pentacene, or6,13-diphenylpentacene; and the N-type semiconductor layer contains anyof 3,4,9,10-perylenetetracarboxylicdianhydride,3,4,9,10-perylenetetracarboxylicdiimide,N,N′-dimethyl-3,4,9,10-perylenetetracarboxylicdiimide,1,4,5,8-naphthalenetetracarboxylicdianhydride, or1,4,5,8-naphthalenetetracarboxylicdiimide.

In the above structure, it is preferable that a third layer containing aconductive material be provided between the P-type semiconductor layerand the N-type semiconductor layer. As the conductive material, indiumtin oxide, indium tin oxide containing silicon or silicon oxide, indiumzinc oxide, indium tin oxide containing tungsten oxide and zinc oxide,or the like is given.

In addition, in the above structure, it is preferable that a third layercontaining a semiconductor material be provided between the P-typesemiconductor layer and the N-type semiconductor layer. As thesemiconductor material, titanium oxide, vanadium oxide, niobium oxide,molybdenum oxide, tungsten oxide, rhenium oxide, ruthenium oxide, cobaltoxide, nickel oxide, zinc oxide, copper oxide, tin oxide, zinc sulfide,gallium nitride, gallium aluminum nitride, or the like is given.

Furthermore, in the above structure, it is preferable that the P-typesemiconductor layer further contains an acceptor material. As theacceptor material, 7,7,8,8-tetracyano-2,3,5,6-tetrafluoroquinodimethane,chloranil, or the like is given. In addition, a transition metal oxideis given. For example, vanadium oxide, niobium oxide, tantalum oxide,chromium oxide, molybdenum oxide, tungsten oxide, manganese oxide,rhenium oxide, or the like can be used.

Furthermore, in the above structure, it is preferable that the N-typesemiconductor layer further contains a donor material. As the donormaterial, an alkali metal, an alkaline earth metal, a rare earth metal,or a metal that belongs to Group 13 of the periodic table is given. Forexample, lithium (Li), cesium (Cs), magnesium (Mg), calcium (Ca),ytterbium (Yb), or indium (In) can be used.

Furthermore, the present invention includes a light emitting devicehaving the above-described light emitting element in its category. Thelight emitting device in the present specification includes an imagedisplay device, a light emitting device, or a light source (including alighting device). In addition, the light emitting device of the presentinvention includes all the following modules: a module in which aconnector such as an PPC (flexible printed circuit), a TAB (tapeautomated bonding) tape or a TCP (tape carrier package) is attached to apanel provided with a light emitting element; a module provided with aprinted wiring board at the end of the TAB tape or the TCP; and a modulein which an IC (integrated circuit) is directly mounted to a lightemitting element by a COG (chip on glass) method.

Furthermore, the present invention includes an electronic device usingthe light emitting element of the present invention for the displayportion in its category. Accordingly, one feature of the electronicdevice of the present invention is to include a display portion providedwith the above-described light emitting element and a controller forcontrolling light emission of the light emitting element.

A light emitting element of the present invention is provided with alayer that absorbs light emission between a light emitting region and anelectrode, therefore, light reflected by the electrode can be reduced,and a high contrast can be realized.

Furthermore, a light emitting device of the present invention has alight emitting element that is excellent in contrast, therefore, a highcontrast can be realized.

Furthermore, the light emitting element of the present invention canimprove the contrast without using a polarizing plate, a quarter-waveplate, or the like outside of the element. For this reason, the contrastcan be improved without an increase in the number of manufacturingsteps. In addition, since the polarizing plate, the quarter-wave plate,or the like is not necessarily used, a light emitting element with ahigh contrast can be manufactured at low costs.

BRIEF DESCRIPTION OF THE DRAWINGS

In the accompanying drawings:

FIG. 1 is a view explaining a light emitting element of the presentinvention;

FIG. 2 is a view explaining a light emitting element of the presentinvention;

FIG. 3 is a view explaining a light emitting element of the presentinvention;

FIG. 4 is a view explaining a light emitting element of the presentinvention;

FIGS. 5A and 5B are views each explaining a light emitting device of thepresent invention;

FIG. 6 is a view explaining a light emitting device of the presentinvention;

FIGS. 7A to 7D are views each explaining an electronic device of thepresent invention;

FIG. 8 is a view explaining a light emitting element of the presentinvention;

FIG. 9 is a view explaining a light emitting element of the presentinvention;

FIG. 10 is a view explaining a light emitting element of Embodiments 1and 2;

FIG. 11 is a graph showing current efficiency-luminance characteristicsof elements manufactured in Embodiment 1;

FIG. 12 is a graph showing current-voltage characteristics of elementsmanufactured in Embodiment 1;

FIG. 13 is a graph showing emission spectrums of elements manufacturedin Embodiment 1;

FIG. 14 is a graph showing absorption spectrums of materials used inEmbodiment 1;

FIG. 15 is a graph showing current efficiency-luminance characteristicsof elements manufactured in Embodiment 2;

FIG. 16 is a graph showing current-voltage characteristics of elementsmanufactured in Embodiment 2;

FIG. 17 is a graph showing emission spectrums of elements manufacturedin Embodiment 2; and

FIG. 18 is a graph showing absorption spectrums of materials used inEmbodiment 2.

DETAILED DESCRIPTION OF THE INVENTION

Embodiment Modes of the present invention will be described in detailbelow with reference to the drawings. However, the present invention isnot limited to the description below and it is to be easily understoodby those skilled in the art that the modes and details can be changed invarious ways without departing from the spirit and scope of the presentinvention. Therefore, the present invention should not be interpreted asbeing limited to the description of Embodiment Modes below.

It is to be noted that, in the present specification, “composition”means not only a simple mixture of two materials but also a mixture of aplurality of materials in a condition where an electric charge is givenand received among the materials.

(Embodiment Mode 1)

A light emitting element of the present invention has a layer containinga light emitting substance interposed between a first electrode and asecond electrode. The layer containing the light emitting substanceincludes a light emitting layer, a first layer, and a second layer. Thefirst electrode has a light-transmitting property, and the first layerand the second layer are interposed between the second electrode and thelight emitting layer. In this embodiment mode, the first layer and thesecond layer that are included in the light emitting element of thepresent invention will be described.

The first layer and the second layer each contain an organic compoundthat has the absorption peak in a visible light region, and are layersthat absorb visible light. The first layer contains a first organiccompound, and the second layer contains a second organic compound. Colorof the first organic compound and color of the second organic compoundare complementary. For this reason, a stack of the first layer and thesecond layer can absorb visible light over a wide wavelength region.Specifically, the first organic compound has the absorption peak in awavelength region of greater than or equal to 380 nm and less than 540nm, and the second organic compound has the absorption peak in awavelength region of greater than or equal to 540 nm and less than orequal to 760 nm.

As the first organic compound contained in the first layer, variousmaterials can be used as long as the materials are organic compoundshaving the absorption peaks in a wavelength region of greater than orequal to 380 nm and less than 540 nm. In particular, an organic compoundexcellent in a carrier transporting property is preferably used.Specifically, 3,4,9,10-perylenetetracarboxylic acid derivatives,1,4,5,8-naphthalenetetracarboxylic acid derivatives, a naphthacenederivatives, nickel complexes, or the like is given. For example,3,4,9,10-perylenetetracarboxylicdianhydride (abbreviation: PTCDA),3,4,9,10-perylenetetracarboxylicdiimide (abbreviation: PTCDI),N,N′-dimethyl-3,4,9,10-perylenetetracarboxylicdiimide (abbreviation:Me-PTCDI), 1,4,5,8-naphthalenetetracarboxylicdianhydride (abbreviation:NTCDA), 1,4,5,8-naphthalenetetracarboxylicdiimide (abbreviation: NTCDI),naphthacene, 5,12-diphenylnaphthacene, rubrene,N,N′-Disalicylideneethylenediaminatonickel (II) (abbreviation: [Ni(salen)]), N,N′-Disalicylidene-o-phenylenediaminatonickel (II)(abbreviation: [Ni (saloph)]), or the like is given. Structural formulasof these organic compounds are shown below.

As the second organic compound contained in the second layer, variousmaterials can be used as long as the materials are organic compoundshaving the absorption peaks in a wavelength region of greater than orequal to 540 nm and less than or equal to 760 nm. In particular, anorganic compound excellent in a carrier transporting property ispreferably used. Specifically, phthalocyanine derivatives, pentacenederivatives, 3,4,9,10-perylenetetracarboxylic-bis-benzimidazolederivatives, violanthrone derivatives, or the like is given. Forexample, phthalocyanine (abbreviation: H₂Pc), copper phthalocyanine(abbreviation: CuPc), zinc phthalocyanine (abbreviation: ZnPc), vanadylphthalocyanine (abbreviation: VOPc), titanyl phthalocyanine(abbreviation: TiOPc), nickel phthalocyanine (abbreviation: NiPc),(1,2,3,4,8,9,10,11,15,16,17,18,22,23,24,25-hexadecafluorophthalocyaninato)copper(abbreviation: F₁₆—CuPc),(1,2,3,4,8,9,10,11,15,16,17,18,22,23,24,25-hexadecafluorophthalocyaninato)zinc(abbreviation: F₁₆—ZnPc), pentacene, 6,13-diphenylpentacene,perfluoropentacene, 3,4,9,10-perylenetetracarboxylic-bis-benzimidazole(abbreviation: PTCBI, also referred to asbisbenzimidazo[2,1-a:2′,1′-a]anthra[2,1,9-def:6,5,10-d′e′f′]diisoquinoline-10,21-dione),violanthrone, isoviolanthrone, or the like is given. Structural formulasof these organic compounds are shown below.

The first layer and the second layer are provided on a side of the lightemitting layer that is opposite the side of the light emitting layerwhere the electrode with a light-transmitting property (the firstelectrode) is provided. In other words, the first layer and the secondlayer are provided on the side opposite to that of the electrode (thefirst electrode) through which light emission from the light emittinglayer is extracted to external. Therefore, in the case where the secondelectrode has high reflectivity, the first layer and the second layercan absorb light emitted from the light emitting layer and light from anexternal source. In this way, light reflected by the second electrodecan be reduced and the contrast of the light emitting element can beimproved.

By making the first layer and/or the second layer thick, the absorbancein a visible light region can be increased. When the absorbance in thevisible light region increases, light emitted from the light emittinglayer can be absorbed better. In this way, the contrast of the lightemitting element can be more improved.

Furthermore, a donor material or an acceptor material may be added tothe first layer and/or the second layer. By adding a donor material oran acceptor material, the conductivity can be improved and the drivingvoltage of the light emitting element can be reduced. In the case wherethe first layer and/or the second layer are/is made thick, especially,an increase in driving voltage can be suppressed by addition of a donormaterial or an acceptor material. In this way, the contrast can befurther improved while suppressing an increase in driving voltage.

As the donor material, an alkali metal, an alkaline earth metal, a rareearth metal, a metal that belongs to Group 13 of the periodic table, oran oxide or carbonate of these can be used. Specifically, lithium (Li),cesium (Cs), magnesium (Mg), calcium (Ca), ytterbium (Yb), indium (In),lithium oxide (LiO_(x)), cesium carbonate (CsCO₃), or the like can beused.

In addition, as the acceptor material,7,7,8,8-tetracyano-2,3,5,6-tetrafluoroquinodimethane (abbreviation:F₄-TCNQ), chloranil, or the like can be given.

Furthermore, as the acceptor material, a transition metal oxide can begiven. In addition, an oxide of metals that belong to Group 4 to Group 8of the periodic table can be given. Specifically, vanadium oxide,niobium oxide, tantalum oxide, chromium oxide, molybdenum oxide,tungsten oxide, manganese oxide, and rhenium oxide are preferable sincetheir electron-accepting property is high. Among these, molybdenum oxideis especially preferable, since it is stable in the air and itshygroscopic property is low so that it can be easily treated.

It is to be noted that the order of stacking the first layer and thesecond layer is not particularly limited. For example, the electrodethat has a light-transmitting property (the first electrode), the lightemitting layer, the first layer, the second layer, and the secondelectrode may be provided in this order. Alternatively, the electrodethat has a light-transmitting property (the first electrode), the lightemitting layer, the second layer, the first layer, and the secondelectrode may be provided in this order.

Furthermore, a layer containing a semiconductor material or conductivematerial may be provided between the first layer and the second layer.As the conductive material, for example, indium tin oxide (ITO), indiumtin oxide containing silicon or silicon oxide, indium zinc oxide (IZO),indium oxide containing tungsten oxide and zinc oxide (IWZO), or thelike is given. In addition, for example, a film of a metal such asaluminum (Al) or silver (Ag) that is formed to have a thickness of 1 to50, preferably approximately 5 to 20 nm, so as to have alight-transmitting property may be used. In addition, as thesemiconductor material, titanium oxide (TiO_(x)), vanadium oxide(VO_(x)), niobium oxide (NbO_(x)), molybdenum oxide (MoO_(x)), tungstenoxide (WO_(x)), rhenium oxide (ReO_(x)), ruthenium oxide (RuO_(x)),cobalt oxide (CoO_(x)), nickel oxide (NiO_(x)), zinc oxide (ZnO_(x)),copper oxide (CuO_(x)), tin oxide (SnO_(x)), zinc sulfide (ZnS), galliumnitride (GaN), gallium aluminum nitride (AlGaN), or the like is given.

Any method, a wet method or a dry method, may be used to form the firstlayer and the second layer. For example, a vacuum evaporation method, anink-jet method, a spin coat method, or the like may be used.

This embodiment mode can be appropriately combined with other embodimentmodes.

(Embodiment Mode 2)

In this embodiment mode, one mode of a light emitting element with thelayer that absorbs visible light described in Embodiment Mode 1 will bedescribed with reference to FIG. 1.

A light emitting element of the present invention has a plurality oflayers between a pair of electrodes. The plurality of layers are acombination of layers formed of a material with a high carrier-injectingproperty and a material with a high carrier-transporting property whichare stacked so that a light emitting region is formed in a region awayfrom the electrodes, that is, recombination of carriers is performed inan area away from the electrodes. Hereinafter, the layers formed betweenthe electrodes will be referred to as layers containing a light emittingsubstance.

In this embodiment mode, a light emitting element includes a firstelectrode 102, a first layer 103, a second layer 104, and a third layer105 which are stacked over the first electrode 102 in order, and asecond electrode 106 provided thereover. It is to be noted that thedescription will be made below regarding the first electrode 102 as ananode and the second electrode 106 as a cathode.

The substrate 101 is used as a base of the light emitting element. Asthe substrate 101, glass, plastic, or the like may be used, for example.Other materials than those may be used, as long as the materialsfunction as a base in the process of manufacturing the light emittingelement.

It is preferable that the first electrode 102 be an electrode with ahigh light-transmitting property. In addition, a metal, an alloy, aconductive compound, or a mixture thereof, each of which has a high workfunction (specifically, 4.0 eV or more), or the like is preferably used.Specifically, for example, indium tin oxide (ITO), indium tin oxidecontaining silicon or silicon oxide, indium zinc oxide (IZO), indiumoxide containing tungsten oxide and zinc oxide (IWZO), or the like isgiven. Such conductive metal oxide films are usually formed bysputtering, but may also be formed by using a sol-gel method or thelike. For example, indium zinc oxide (IZO) can be formed by a sputteringmethod using a target in which zinc oxide of 1 to 20 wt % is added toindium oxide. Indium oxide containing tungsten oxide and zinc oxide(IWZO) can be formed by a sputtering method using a target containingtungsten oxide of 0.5 to 5 wt % and zinc oxide of 0.1 to 1 wt % withrespect to indium oxide. Other than these, gold (Au), platinum (Pt),nickel (Ni), tungsten (W), chromium (Cr), molybdenum (Mo), iron (Fe),cobalt (Co), copper (Cu), palladium (Pd), a nitride of a metal material(such as titanium nitride: TiN) or the like may be used to form a filmhaving a thickness of 1 to 50 nm, preferably approximately 5 to 20 nm,so as to serve as the first electrode 102.

The first layer 103 is a layer that contains a light emitting substance.The first layer 103 may be structured as a single layer, or a pluralityof layers may be stacked to form the first layer 103. The layeredstructure is not particularly limited, and layers each formed of amaterial with a high electron-transporting property, a material with ahigh hole-transporting property, a material with a highelectron-injecting property, a material with a high hole-injectingproperty, a bipolar material (a material with high electron-transportingand hole-transporting properties) and the like may be appropriatelycombined. For example, a hole-injecting layer, a hole-transportinglayer, a hole-blocking layer, a light emitting layer, anelectron-transporting layer, an electron-injecting layer, and the likemay be appropriately combined to constitute the first layer 103.Specific materials to form each of the layers will be given below.

A hole-injecting layer is a layer that contains a material with a highhole-injecting property. As the material with a high hole-injectingproperty, molybdenum oxide (MoO_(x)), vanadium oxide (VO_(x)), rutheniumoxide (RuO_(x)), tungsten oxide (WOO, manganese oxide (MnO_(x)), or thelike may be used. In addition, it is possible to use aphthalocyanine-based compound such as phthalocyanine (H₂Pc) or copperphthalocyanine (CuPc), a high molecule such asPoly(3,4-ethylenedioxythiophene)/poly(styrenesulfonate) (PEDOT/PSS), orthe like to form the hole-injecting layer.

Alternatively, as the hole-injecting layer, a composite material of amaterial with a high hole-transporting property containing an acceptormaterial may be used. It is to be noted that, by using the material witha high hole-transporting property containing an acceptor material, amaterial used to form an electrode may be selected regardless of itswork function. In other words, besides a material with a high workfunction, a material with a low work function may also be used as thefirst electrode 102. As the acceptor material,7,7,8,8-tetracyano-2,3,5,6-tetrafluoroquinodimethane (abbreviation:F₄-TCNQ), chloranil, or the like can be given. In addition, a transitionmetal oxide is given. In addition, an oxide of metals that belong toGroup 4 to Group 8 of the periodic table can be given. Specifically,vanadium oxide, niobium oxide, tantalum oxide, chromium oxide,molybdenum oxide, tungsten oxide, manganese oxide, and rhenium oxide arepreferable since their electron-accepting property is high. Among these,molybdenum oxide is especially preferable since it is stable in the airand its hygroscopic property is low so that it can be easily treated.

As the organic compound for the composite material, various compoundssuch as an aromatic amine compound, carbazole derivatives, aromatichydrocarbon, and a high-molecular compound (such as oligomer, dendrimer,or polymer) can be used. The organic compound used for the compositematerial is preferably an organic compound having a highhole-transporting property. Specifically, a material having a holemobility of 10⁻⁶ cm²/Vs or higher is preferably used. However, othermaterials than those may also be used as long as the materials havehigher hole-transporting properties than electron-transportingproperties. The organic compounds which can be used for the compositematerial will be specifically shown below.

For example, the followings can be given as the aromatic amine compound:N,N′-bis(4-methylphenyl)(p-tolyl)-N,N′-diphenyl-p-phenylenediamine(abbreviation: DTDPPA);4,4′-bis[N-(4-diphenylaminophenyl)-N-phenylamino]biphenyl (abbreviation:DPAB);4,4′-bis(N-[4-[N-(3-methylphenyl)-N′-phenylamino]phenyl]-N-phenylamino)biphenyl(abbreviation: DNTPD);1,3,5-tris[N-(4-diphenylaminophenyl)-N-phenylamino]benzene(abbreviation: DPA3B); and the like.

As the carbazole derivatives which can be used for the compositematerial, the followings can be given specifically:3-[N-(9-phenylcarbazole-3-yl)-N-phenylamino]-9-phenylcarbazole(abbreviation: PCzPCA1);3,6-bis[N-(9-phenylcarbazole-3-yl)-N-phenylamino]-9-phenylcarbazole(abbreviation: PCzPCA2);3-[N-(1-naphtyl)-N-(9-phenylcarbazole-3-yl)amino]-9-phenylcarbazole(abbreviation: PCzPCN1); and the like.

Moreover, 4,4′-di(N-carbazolyl)biphenyl (abbreviation: CBP);1,3,5-tris[4-(N-carb azolyl)phenyl]benzene (abbreviation: TCPB);9-[4-(N-carbazolyl)]phenyl-10-phenylanthracene (abbreviation: CzPA);1,4-bis[4-(N-carbazolyl)phenyl]-2,3,5,6-tetraphenylbenzene; or the likecan also be used.

As the aromatic hydrocarbon which can be used for the compositematerial, the followings can be given for example:2-tert-butyl-9,10-di(2-naphthyl)anthracene (abbreviation: t-BuDNA);2-tert-butyl-9,10-di(1-naphthyl)anthracene,9,10-bis(3,5-diphenylphenyl)anthracene (abbreviation: DPPA);2-tert-butyl-9,10-bis(4-phenylphenyl)anthracene (abbreviation: t-BuDBA);9,10-di(2-naphthyl)anthracene (abbreviation: DNA);9,10-diphenylanthracene (abbreviation: DPAnth); 2-tert-butylanthracene(abbreviation: t-BuAnth); 9,10-bis(4-methyl-1-naphthyl)anthracene(abbreviation: DMNA);9,10-bis[2-(1-naphthyl)phenyl]-2-tert-butyl-anthracene;9,10-bis[2-(1-naphthyl)phenyl]anthracene;2,3,6,7-tetramethyl-9,10-di(1-naphthyl)anthracene;2,3,6,7-tetramethyl-9,10-di(2-naphthyl)anthracene; 9,9′-bianthryl;10,10′-diphenyl-9,9′-bianthryl;10,10′-bis(2-phenylphenyl)-9,9′-bianthryl;10,10′-bis[(2,3,4,5,6-pentaphenyl)phenyl]-9,9′-bianthryl; anthracene;tetracene; rubrene; perylene; 2,5,8,11-tetra(tert-butyl)perylene; andthe like. Besides those, pentacene, coronene, or the like can also beused. In particular, the aromatic hydrocarbon which has a hole mobilityof 1×10⁻⁶ cm²/Vs or higher and which has 14 to 42 carbon atoms isparticularly preferable.

The aromatic hydrocarbon which can be used for the composite materialmay have a vinyl skeleton. As the aromatic hydrocarbon having a vinylgroup, the followings are given for example:4,4′-bis(2,2-diphenylvinyl)biphenyl (abbreviation: DPVBi);9,10-bis[4-(2,2-diphenylvinyl)phenyl]anthracene (abbreviation: DPVPA);and the like.

Moreover, a high molecular compound such as poly(N-vinylcarbazole)(abbreviation: PVK) or poly(-vinyltriphenylamine) (abbreviation: PVTPA)can also be used.

The hole-transporting layer is a layer that contains a material with ahigh hole-transporting property. As the material with a highhole-transporting property, for example, an aromatic amine compound suchas 4,4′-bis[N-(1-naphthyl)-N-phenylamino]biphenyl (abbreviation: NPB orα-NPD),N,N′-bis(3-methylphenyl)-N,N′-diphenyl-[1,1′-biphenyl]-4,4′-diamine(abbreviation: TPD), 4,4′,4″-tris(N,N-diphenylamino)triphenylamine(abbreviation: TDATA),4,4′,4″-tris[N-(3-methylphenyl)-N-phenylamino]triphenylamine(abbreviation: MTDATA), or4,4′-bis[N-(spiro-9,9′-bifluoren-2-yl)-N-phenylamino]biphenyl(abbreviation: BSPB) can be used. These materials mainly are materialseach having a hole mobility of 10⁻⁶ cm²/Vs or higher. However, othermaterials than these may also be used as long as the hole-transportingproperties thereof are higher than the electron-transporting properties.The layer containing a material with a high hole-transporting propertyis not limited to a single layer, and two or more layers containing theaforementioned materials may be stacked.

The light emitting layer is a layer that contains a material with a highlight emitting property, and can be made of various kinds of materials.For example, a material with a high light emitting property is freelycombined with a material with a high carrier-transporting property andgood film quality (that is, a material difficult to be crystallized),such as tris(8-quinolinolato)aluminum (abbreviation: Alq),2-tert-butyl-9,10-di(2-naphthyl)anthracene (abbreviation: t-BuDNA), or4,4′-bis[N-(1-naphthyl)-N-phenylamino]biphenyl (abbreviation: NPB).Specifically, the material with a high light emitting property may be asinglet light emitting material (fluorescent material) such asN,N′-dimethylquinacridone (abbreviation: DMQd),N,N′-diphenylquinacridone (abbreviation: DPQd), coumarin 6,4-(dicyanomethylene)-2-methyl-6-(p-dimethylaminostyryl)-4H-pyran(abbreviation: DCM1),4-(dicyanomethylene)-2-methyl-6-[2-(julolidine-9-yl)vinyl]-4H-pyran(abbreviation: DCM2), 9,10-diphenylanthracene, 5,12-diphenyltetracene(abbreviation: DPT), perylene, or rubrene, or a triplet light emittingmaterial (phosphorescent material) such asbis[2-(2′-benzo[4,5-a]thienyl)pyridinato-N,C^(3′)]iridium(acetylacetonate)(abbreviation: Ir(btp)₂(acac)). However, since Alq and DNA are materialswith high light emitting properties, the third layer 105 may be formedof only one of these materials.

The electron-transporting layer is a layer that contains a material witha high electron-transporting property. For example, a layer containing ametal complex having a quinoline skeleton or a benzoquinoline skeleton,such as tris(8-quinolinolato)aluminum (abbreviation: Alq),tris(4-methyl-8-quinolinolato)aluminum (abbreviation: Almq₃),bis(10-hydroxybenzo[h]-quinolinato)beryllium (abbreviation: BeBq₂), orbis(2-methyl-8-quinolinolato)(4-phenylphenolato)aluminum (abbreviation:BAlq) can be used. Alternatively, a metal complex having anoxazole-based or thiazole-based ligand, such asbis[2-(2-hydroxyphenyl)benzoxazolato]zinc (abbreviation: Zn(BOX)₂) orbis[2-(2-hydroxyphenyl)-benzothiazolato]zinc (abbreviation: Zn(BTZ)₂)can be used. Besides the metal complexes,2-(4-biphenylyl)-5-(4-tert-butylphenyl)-1,3,4-oxadiazole (abbreviation:PBD), 1,3-bis [5-(p-tert-butylphenyl)-1,3,4-oxadiazole-2-yl]benzene(abbreviation: OXD-7),3-(4-biphenylyl)-4-phenyl-5-(4-tert-butylphenyl)-1,2,4-triazole(abbreviation: TAZ), bathophenanthroline (abbreviation: BPhen),bathocuproine (abbreviation: BCP), or the like can also be used. Thematerials mentioned here mainly are materials each having an electronmobility of 10⁻⁶ cm²/Vs or higher. The electron-transporting layer maybe formed of other materials than those described above as long as thematerials have higher electron-transporting properties thanhole-transporting properties. Furthermore, the electron-transportinglayer is not limited to a single layer, and two or more layers made ofthe aforementioned materials may be stacked.

In addition, an electron-injecting layer may be provided. As theelectron-injecting layer, an alkali metal, an alkaline earth metal, or acompound thereof such as lithium fluoride (LiF), cesium fluoride (CsF),or calcium fluoride (CaP₂) may be used. For example, a layer of amaterial having an electron-transporting property containing an alkalimetal, an alkaline earth metal, or a compound thereof, such as Alq whichcontains magnesium (Mg), may be used. By using a layer of a materialhaving an electron-transporting property containing an alkali metal oran alkaline earth metal, electron injection from an N-type semiconductorlayer as the second layer 104 is performed efficiently, which ispreferable.

The second layer 104 is an N-type semiconductor layer. As the secondlayer 104, the organic compound described in Embodiment Mode 1 which hasthe absorption peak in a visible light region may be used to form alayer functioning as an N-type semiconductor. The second layer 104 isnot limited to a single layer, and a plurality of layers may be stackedto form the second layer 104.

The third layer 105 is a P-type semiconductor layer. As the third layer105, the organic compound described in Embodiment Mode 1 which has theabsorption peak in a visible light region may be used to form a layerfunctioning as a P-type semiconductor. The third layer 105 is notlimited to a single layer, and a plurality of layers may be stacked toform the third layer 105.

It is preferable that color of the second layer 104 and color of thethird layer 105 be complementary. In other words, it is preferable thatone of the material constituting the second layer 104 or the materialconstituting the third layer 105 have the absorption peak in awavelength region of greater than or equal to 380 nm and less than 540nm and the other have the absorption peak in a wavelength region ofgreater than or equal to 540 nm and less than or equal to 760 nm.

More specifically, in the case where a material that has the absorptionpeak in a wavelength region of greater than or equal to 380 nm and lessthan 540 nm is used as the second layer 104, it is preferable that amaterial that has the absorption peak in a wavelength region of greaterthan or equal to 540 nm and less than or equal to 760 nm be used as thethird layer 105. In the case of a combination as the above, for example,3,4,9,10-perylenetetracarboxylicdianhydride (abbreviation: PTCDA),3,4,9,10-perylenetetracarboxylicdiimide (abbreviation: PTCDI),N,N′-dimethyl-3,4,9,10-perylenetetracarboxylicdiimide (abbreviation:Me-PTCDI), 1,4,5,8-naphthalenetetracarboxylicdianhydride (abbreviation:NTCDA), 1,4,5,8-naphthalenetetracarboxylicdiimide (abbreviation: NTCDI),or the like may be used as the second layer 104. As the third layer 105,phthalocyanine (abbreviation: H₂Pc), copper phthalocyanine(abbreviation: CuPc), zinc phthalocyanine (abbreviation: ZnPc), vanadylphthalocyanine (abbreviation: VOPc), titanyl phthalocyanine(abbreviation: TiOPc), nickel phthalocyanine (abbreviation: NiPc),pentacene, 6,13-diphenylpentacene, or the like may be used.

Alternatively, in the case where a material that has the absorption peakin a wavelength region of greater than or equal to 540 nm and less thanor equal to 760 nm is used as the second layer 104, it is preferablethat a material that has the absorption peak in a wavelength region ofgreater than or equal to 380 nm and less than 540 nm be used as thethird layer 105. In the case of a combination as the above, for example,(1,2,3,4,8,9,10,11,15,16,17,18,22,23,24,25-hexadecafluorophthalocyaninato)copper(abbreviation: F₁₆—CuPc),(1,2,3,4,8,9,10,11,15,16,17,18,22,23,24,25-hexadecafluorophthalocyaninato)zinc(abbreviation: F₁₆—ZnPc), perfluoropentacene,3,4,9,10-perylenetetracarboxylic-bis-benzimidazole (abbreviation:PTCBI), or the like may be used as the second layer 104. As the thirdlayer 105, naphthacene, 5,12-diphenylnaphthacene, rubrene, or the likemay be used.

Due to the structure as the above, a stack of the second layer 104 andthe third layer 105 can absorb visible light over a wide wavelengthregion. In this way, light reflected by the second electrode 106 can bereduced and the contrast of the light emitting element can be improved.

It is to be noted that the N-type semiconductor layer may be furtheradded with a donor material. The conductivity of the N-typesemiconductor layer can be increased by addition of a donor material,whereby the driving voltage of the light emitting element can belowered. As the donor material, an alkali metal, an alkaline earthmetal, a rare earth metal, a metal that belongs to Group 13 of theperiodic table, or an oxide or carbonate of them may be used.Specifically, lithium (Li), cesium (Cs), magnesium (Mg), calcium (Ca),ytterbium (Yb), indium (In), lithium oxide (LiO_(x)), cesium carbonate(CsCO₃), or the like is preferably used.

Furthermore, the P-type semiconductor layer may be further added with anacceptor material. The conductivity of the P-type semiconductor layercan be increased by addition of an acceptor material, whereby thedriving voltage of the light emitting element can be lowered. As theacceptor material, 7,7,8,8-tetracyano-2,3,5,6-tetrafluoroquinodimethane(abbreviation: F₄-TCNQ), chloranil, or the like can be given.Furthermore, as the acceptor material, a transition metal oxide can begiven. In addition, an oxide of metals that belong to Group 4 to Group 8of the periodic table can be given. Specifically, vanadium oxide,niobium oxide, tantalum oxide, chromium oxide, molybdenum oxide,tungsten oxide, manganese oxide, and rhenium oxide are preferable sincetheir electron-accepting property is high. Among these, molybdenum oxideis especially preferable, since it is stable in the air and itshygroscopic property is low so that it can be easily treated.

Furthermore, by using a P-type semiconductor layer to which an acceptormaterial is added and/or an N-type semiconductor layer to which a donormaterial is added, an increase of a driving voltage can be suppressedeven when the P-type semiconductor layer and/or the N-type semiconductorlayer are/is formed to be thick. Accordingly, by following the P-typesemiconductor layer and/or the N-type semiconductor layer to be thick,short-circuiting caused by a minute foreign object, an impact, or thelike can be prevented; whereby a light emitting element with a highreliability can be obtained. The film thickness between the electrodesof a general light emitting element is 100 to 150 nm, however, in thecase of a light emitting element using the P-type semiconductor layerand the N-type semiconductor layer, it can be 100 to 500 nm, preferably,200 to 500 nm thick, for example.

In addition, a P-type semiconductor layer to which an acceptor materialis added and an N-type semiconductor layer to which a donor material isadded have small contact resistance with respect to electrodes. For thisreason, the electrode materials can be selected without consideringtheir work functions or the like; therefore, options of the electrodematerials are increased.

As the second electrode 106, various metals, an alloy, a conductivecompound, a mixture thereof, or the like can be used. An example thereofis indium tin oxide (ITO), indium tin oxide containing silicon orsilicon oxide, indium zinc oxide (IZO), iridium oxide containingtungsten oxide and zinc oxide (IWZO), or the like. These conductivemetal oxide films are generally foaled by sputtering. For example,indium zinc oxide (IZO) can be formed by a sputtering method using atarget in which zinc oxide of 1 to 20 wt % is added to indium oxide.Indium oxide containing tungsten oxide and zinc oxide (IWZO) can beformed by a sputtering method using a target containing tungsten oxideof 0.5 to 5 wt % and zinc oxide of 0.1 to 1 wt % with respect to indiumoxide. Besides these, gold (Au), platinum (Pt), nickel (Ni), tungsten(W), chromium (Cr), molybdenum (Mo), iron (Fe), cobalt (Co), titanium(Ti), copper (Cu), palladium (Pd), aluminum (Al), aluminum-silicon(Al—Si), aluminum-titanium (Al—Ti), aluminum-silicon-copper (Al—Si—Cu),a nitride of the metal material (such as TiN), or the like can be used.

Various methods can be used for forming the first layer 103, the secondlayer 104, and the third layer 105. For example, a vacuum evaporationmethod, an ink-jet method, a spin coat method, or the like may be used.Furthermore, each electrode or each layer may be formed by a differentfilm formation method.

The light emitting element of the present invention which has thestructure as the above emits light when a current flows due to potentialdifference generated between the first electrode 102 and the secondelectrode 106 and holes and electrons are recombined in the first layer103 that is a layer containing a material with a high light emittingproperty. That is, the light emitting element of the present inventionhas a structure in which a light emitting region is formed in the firstlayer 103.

In the light emitting element shown in FIG. 1, light emission isextracted to external through the first electrode 102. Therefore, thefirst electrode 102 is formed using a light-transmitting material.Accordingly, light emission is extracted to external through the firstelectrode 102 from the substrate side.

It is to be noted that the structure of layers provided between thefirst electrode 102 and the second electrode 106 is not limited to thestructure described above. Structures other than the above-described onemay be employed as long as a region where holes and electrons arerecombined is provided in an area away from the first electrode 102 andthe second electrode 106 so as to suppress quenching caused when a lightemitting region and a metal are close to each other, and as long as thesecond layer 104 and the third layer 105 which absorb visible light areprovided.

In other words, the layered structure is not particularly limited, andlayers each formed of a material with a high electron-transportingproperty, a material with a high hole-transporting property, a materialwith a high electron-injecting property, a material with a highhole-injecting property, a bipolar material (a material with highelectron-transporting and hole-transporting properties) or the like maybe appropriately combined with the second layer 104 and the third layer105 which absorb visible light. Alternatively, a structure in which alayer formed of a silicon oxide film or the like is provided over thefirst electrode 102 so as to control a portion where recombination ofcarriers is performed may be employed.

Alternatively, a structure in which layers are stacked in the orderopposite to that of FIG. 1 and light emission is extracted to externalfrom the side opposite to the substrate may be employed. A lightemitting element shown in FIG. 2 has a structure in which the thirdlayer 105 that is a P-type semiconductor layer, the second layer 104that is an N-type semiconductor layer, the first layer 103 that is alayer containing a light emitting substance, and the first electrode 102that functions as an anode are stacked in this order over the secondelectrode 106 that functions as a cathode. In the case where thestructure shown in FIG. 2 is employed, light emission from the firstlayer 103 is extracted to external from the first electrode side whichis opposite to the substrate 101.

Furthermore, as shown in FIG. 8, a fourth layer 107 may be providedbetween the second layer 104 and the third layer 105. Through provisionof the fourth layer 107, the driving voltage can be lowered. As amaterial for forming the fourth layer 107, a semiconductor material or aconductive material may be used. As the conductive material, forexample, indium tin oxide (ITO), indium tin oxide containing silicon orsilicon oxide, indium zinc oxide (IZO), indium oxide containing tungstenoxide and zinc oxide (IWZO), or the like can be given. In addition, forexample, a film of a metal such as aluminum (Al) or silver (Ag) that isformed to have a thickness of 1 to 50 nm, preferably approximately 5 to20 nm, so as to have a light-transmitting property may be used. Inaddition, as the semiconductor material, titanium oxide (TiO_(x)),vanadium oxide (VO_(x)), niobium oxide (NbO_(x)), molybdenum oxide(MoO_(x)), tungsten oxide (WOO, rhenium oxide (ReO_(x)), ruthenium oxide(RuO_(x)), cobalt oxide (CoO_(x)), nickel oxide (NiO_(x)), zinc oxide(ZnO_(x)), copper oxide (CuO_(x)), tin oxide (SnO_(x)), zinc sulfide(ZnS), gallium nitride (GaN), gallium aluminum nitride (AlGaN), or thelike is given.

In this embodiment mode, the light emitting element is manufactured overa substrate of glass, plastic, or the like. By manufacturing a pluralityof light emitting elements like this over one substrate, a passive lightemitting device can be manufactured. In addition, a thin film transistor(TFT) may be formed over a substrate of glass, plastic, or the like anda light emitting element may be manufactured over an electrode that iselectrically connected to the TFT. In this way, an active matrix lightemitting device in which the TFT controls the drive of the lightemitting element can be manufactured. It is to be noted that thestructure of the TFT is not particularly limited. A staggered TFT or aninversely staggered TFT may be employed. In addition, a driver circuitformed over a TFT substrate may be formed using N-type and P-type TFTs,or using either N-type or P-type TFTs. Crystallinity of a semiconductorfilm used for the TFT is not particularly limited, either. An amorphoussemiconductor film may be used, or a crystalline semiconductor film maybe used.

A light emitting element of the present invention has the second layer104 and the third layer 105 which absorb visible light between the lightemitting layer and the second electrode. Accordingly, light reflected bythe second electrode can be reduced and the contrast can be improved.

Furthermore, optical design of the light emitting element of the presentinvention can be performed without considering light reflected by thesecond electrode, which means that the optical design can be performedmore easily.

Furthermore, the P-type semiconductor layer and the N-type semiconductorlayer used for the light emitting element of the present invention canbe formed by vacuum evaporation. When a layer containing a lightemitting substance is formed by vacuum evaporation, any of the layerscan be formed in the same vacuum device, and the light emitting elementcan be formed in a consistent vacuum. Accordingly, attachment of aminute foreign object in the manufacturing process can be prevented anda yield can be improved.

This embodiment mode can be appropriately combined with other embodimentmodes.

(Embodiment Mode 3)

In this embodiment mode, a light emitting element that has a differentstructure from the structure described in Embodiment Mode 2 will bedescribed with reference to FIG. 3.

In this mode, the light emitting element includes a first electrode 302,a first layer 303, a second layer 304, and a third layer 305 that arestacked over the first electrode 302 in order, and a second electrode306 provided thereover. It is to be noted that the description will bemade below regarding the first electrode 302 as a cathode and the secondelectrode 306 as an anode, in this mode.

The substrate 301 is used as a base of the light emitting element. Asthe substrate 301, glass, plastic, or the like may be used, for example.Other materials than those may be used, as long as the materialsfunction as a base in the process of manufacturing the light emittingelement.

It is preferable that the first electrode 302 be an electrode with ahigh light-transmitting property. In addition, a metal, an alloy, aconductive compound, or a mixture thereof, each of which has a low workfunction (specifically, 3.8 eV or less), or the like is preferably used.Specifically, an element that belongs to Group 1 or Group 2 of theperiodic table, that is, an alkali metal such as lithium (Li) or cesium(Cs), an alkaline earth metal such as magnesium (Mg), calcium (Ca), orstrontium (Sr), an alloy containing these (such as an MgAg alloy or anAlLi alloy), or the like may be used to form a thin film so as totransmit light, as the first electrode 302. Alternatively, a stack of ametal thin film and a transparent conductive film (indium tin oxide(ITO), indium tin oxide containing silicon or silicon oxide, indium zincoxide (IZO), indium oxide containing tungsten oxide and zinc oxide(IWZO), or the like) can be used. For example, a film of an AlLi alloy,an MgAg alloy, or the like which is formed with a thickness of 1 to 50nm, preferably approximately 5 to 20 nm, can be used as the firstelectrode 302.

The first layer 303 is a layer that contains a light emitting substance.The first layer 303 may be structured as a single layer, or a pluralityof layers may be stacked to form the first layer 303. The layeredstructure is not particularly limited, and layers each formed of amaterial with a high electron-transporting property, a material with ahigh hole-transporting property, a material with a highelectron-injecting property, a material with a high hole-injectingproperty, a bipolar material (a material with high electron-transportingand hole-transporting properties) or the like may be appropriatelycombined. For example, a hole-injecting layer, a hole-transportinglayer, a hole-blocking layer, a light emitting layer, anelectron-transporting layer, an electron-injecting layer, and the likemay be appropriately combined to constitute the first layer 103.Specific materials to form each of the layers will be given below.

The electron-injecting layer is a layer containing a material with ahigh electron-injecting property. As the material with a highelectron-injecting property, the materials shown in Embodiment Mode 2may be used. Specifically, an alkali metal, an alkaline earth metal, ora compound thereof such as lithium fluoride (LiF), cesium fluoride(CsF), or calcium fluoride (CaF₂) may be used. For example, a layer of amaterial having an electron-transporting property containing an alkalimetal, an alkaline earth metal, or a compound thereof, such as Alq whichcontains magnesium (Mg), may be used. As an electron-injecting layer, byusing a layer of a material having an electron-transporting propertycontaining an alkali metal or an alkaline earth metal, a material forforming an electrode can be selected without depending on a workfunction of the electrode. In other words, not only a material with alow work function but also a material with a high work function may beused as the first electrode 302.

The electron-transporting layer is a layer containing a material with ahigh electron-transporting property. As the material with a highelectron-transporting property, the materials shown in Embodiment Mode 2may be used.

The light emitting layer is a layer containing a material with a highlight emitting property, and various materials may be used for the lightemitting layer. Specifically, the materials shown in Embodiment Mode 2may be used.

The hole-transporting layer is a layer containing a material with a highhole-transporting property. As the material with a highhole-transporting property, the materials shown in Embodiment Mode 2 maybe used.

In addition, the hole-injecting layer may be provided. As a material forforming the hole-injecting layer, the materials shown in Embodiment Mode2 may be used.

The second layer 304 is a P-type semiconductor layer. As the secondlayer 304, the organic compound that has the absorption peak in avisible light region shown in Embodiment Mode 1 may be used so as toform a layer functioning as a P-type semiconductor. The second layer 304is not limited to a single layer, and may have a structure in which aplurality of layers is stacked.

The third layer 305 is an N-type semiconductor layer. As the third layer305, the organic compound that has the absorption peak in a visiblelight region shown in Embodiment Mode 1 may be used so as to form alayer functioning as an N-type semiconductor. The third layer 305 is notlimited to a single layer, and may have a structure in which a pluralityof layers is stacked.

It is preferable that color of the second layer 304 and color of thethird layer 305 be complementary. In other words, it is preferable thatone of the material constituting the second layer 304 or the materialconstituting the third layer 305 have the absorption peak in awavelength region of greater than or equal to 380 nm and less than 540nm and the other have the absorption peak in a wavelength region ofgreater than or equal to 540 nm and less than or equal to 760 nm.

More specifically, in the case where a material that has the absorptionpeak in a wavelength region of greater than or equal to 380 nm and lessthan 540 nm is used as the second layer 304, it is preferable that amaterial that has the absorption peak in a wavelength region of greaterthan or equal to 540 nm and less than or equal to 760 nm be used as thethird layer 305. In the case of a combination as the above, for example,naphthacene, 5,12-diphenylnaphthacene, rubrene, or the like may be usedfor the second layer 304. As the third layer 305,(1,2,3,4,8,9,10,11,15,16,17,18,22,23,24,25-hexadecafluorophthalocyaninato)copper(abbreviation: F₁₆—CuPc),(1,2,3,4,8,9,10,11,15,16,17,18,22,23,24,25-hexadecafluorophthalocyaninato)zinc(abbreviation: F₁₆—ZnPc),3,4,9,10-perylenetetracarboxylic-bis-benzimidazole (abbreviation:PTCBI), perfluoropentacene, or the like may be used.

Alternatively, in the case where a material that has the absorption peakin a wavelength region of greater than or equal to 540 nm and less thanor equal to 760 nm is used as the second layer 304, it is preferablethat a material that has the absorption peak in a wavelength region ofgreater than or equal to 380 nm and less than 540 nm be used as thethird layer 305. In the case of a combination as the above, for example,phthalocyanine (abbreviation: H₂Pc), copper phthalocyanine(abbreviation: CuPc), zinc phthalocyanine (abbreviation: ZnPc), vanadylphthalocyanine (abbreviation: VOPc), titanyl phthalocyanine(abbreviation: TiOPc), nickel phthalocyanine (abbreviation: NiPc),pentacene, 6,13-diphenylpentacene, or the like may be used for thesecond layer 304. For the third layer 305,3,4,9,10-perylenetetracarboxylicdianhydride (abbreviation: PTCDA),3,4,9,10-perylenetetracarboxylicdiimide (abbreviation: PTCDI),N,N′-dimethyl-3,4,9,10-perylenetetracarboxylicdiimide (abbreviation:Me-PTCDI), 1,4,5,8-naphthalenetetracarboxylicdianhydride (abbreviation:NTCDA), 1,4,5,8-naphthalenetetracarboxylicdiimide (abbreviation: NTCDI),or the like may be used.

Due to the structure as the above, a stack of the second layer 304 andthe third layer 305 can absorb light emitted from the first layer 303.In this way, light reflected by the second electrode 306 can be reducedand the contrast of the light emitting element can be improved.

It is to be noted that the N-type semiconductor layer may be furtheradded with a donor material. The conductivity of the N-typesemiconductor layer can be increased by addition of a donor material,whereby the driving voltage of the light emitting element can belowered. As the donor material, an alkali metal, an alkaline earthmetal, a rare earth metal, a metal that belongs to Group 13 of theperiodic table, or an oxide or carbonate of them may be used.Specifically, lithium (Li), cesium (Cs), magnesium (Mg), calcium (Ca),ytterbium (Yb), indium (In), lithium oxide (LiO_(x)), cesium carbonate(CsCO₃), or the like is preferably used.

Furthermore, the P-type semiconductor layer may be further added with anacceptor material. The conductivity of the P-type semiconductor layercan be increased by addition of an acceptor material, whereby thedriving voltage of the light emitting element can be lowered.Furthermore, contact resistance of electrodes can be reduced by additionof the acceptor material. For this reason, the electrode materials canbe selected without considering their work functions or the like;therefore, options of the electrode materials are increased. As theacceptor material, 7,7,8,8-tetracyano-2,3,5,6-tetrafluoroquinodimethane(abbreviation: F₄-TCNQ), chloranil, or the like can be given.Furthermore, as the acceptor material, a transition metal oxide can begiven. In addition, an oxide of metals that belong to Group 4 to Group 8of the periodic table can be given. Specifically, vanadium oxide,niobium oxide, tantalum oxide, chromium oxide, molybdenum oxide,tungsten oxide, manganese oxide, and rhenium oxide are preferable sincetheir electron-accepting property is high. Among these, molybdenum oxideis especially preferable, since it is stable in the air and itshygroscopic property is low so that it can be easily treated.

Furthermore, by using a P-type semiconductor layer to which an acceptormaterial is added and/or an N-type semiconductor layer to which a donormaterial is added, an increase of a driving voltage can be suppressedeven when the P-type semiconductor layer and/or the N-type semiconductorlayer are/is formed to be thick. Accordingly, by forming the P-typesemiconductor layer and/or the N-type semiconductor layer to be thick,short-circuiting caused by a minute foreign object, an impact, or thelike can be prevented; whereby a light emitting element with a highreliability can be obtained. The film thickness between the electrodesof a general light emitting element is 100 to 150 nm, however, in thecase of a light emitting element using the P-type semiconductor layerand the N-type semiconductor layer, it can be 100 to 500 nm, preferably,200 to 500 nm thick, for example.

In addition, a P-type semiconductor layer to which an acceptor materialis added and an N-type semiconductor layer to which a donor material isadded have small contact resistance with respect to electrodes. For thisreason, the electrode materials can be selected without consideringtheir work functions or the like; therefore, options of the electrodematerials are increased.

As the second electrode 306, various metals, an alloy, a conductivecompound, or a mixed metal, compound, or alloy thereof can be used. Anexample thereof is indium tin oxide (ITO), indium tin oxide containingsilicon or silicon oxide, indium zinc oxide (IZO), indium oxidecontaining tungsten oxide and zinc oxide (IWZO), or the like. Theseconductive metal oxide films are generally formed by sputtering. Forexample, indium zinc oxide (IZO) can be formed by a sputtering methodusing a target in which zinc oxide of 1 to 20 wt % is added to indiumoxide. Indium tin oxide containing tungsten oxide and zinc oxide (IWZO)can be fainted by a sputtering method using a target containing tungstenoxide of 0.5 to 5 wt % and zinc oxide of 0.1 to 1 wt % with respect toindium oxide. Besides these, gold (Au), platinum (Pt), nickel (Ni),tungsten (W), chromium (Cr), molybdenum (Mo), iron (Fe), cobalt (Co),titanium (Ti), copper (Cu), palladium (Pd), aluminum (Al),aluminum-silicon (Al—Si), aluminum-titanium (Al—Ti),aluminum-silicon-copper (Al—Si—Cu), a nitride of the metal material(such as TiN), or the like can be used.

The method for forming the first layer 303, the second layer 304, andthe third layer 305 may be other than the above-described evaporationmethod. For example, an ink-jet method, a spin coat method, or the likemay be used. Furthermore, each electrode or each layer may be formed bya different film formation method.

The light emitting element of the present invention which has thestructure as the above emits light when a current flows due to potentialdifference generated between the first electrode 302 and the secondelectrode 306 and holes and electrons are recombined in the first layer303 that is a layer containing a material with a high light emittingproperty. That is, the light emitting element of the present inventionhas a structure in which a light emitting region is formed in the firstlayer 303.

In the light emitting element shown in FIG. 3, light emission isextracted to external through the first electrode 302. Therefore, thefirst electrode 302 is formed using a light-transmitting material.Accordingly, light emission is extracted to external through the firstelectrode 302 from the substrate side.

It is to be noted that the structure of layers provided between thefirst electrode 302 and the second electrode 306 is not limited to thestructure described above. Structures other than the above-described onemay be employed as long as a region where holes and electrons arerecombined is provided in an area away from the first electrode 302 andthe second electrode 306 so as to suppress quenching caused when a lightemitting region and a metal are close to each other, and as long as thesecond layer 304 and the third layer 305 which absorb visible light areprovided.

In other words, the layered structure is not particularly limited, andlayers each formed of a material with a high electron-transportingproperty, a material with a high hole-transporting property, a materialwith a high electron-injecting property, a material with a highhole-injecting property, a bipolar material (a material with highelectron-transporting and hole-transporting properties) and the like maybe appropriately combined with the second layer 304 and the third layer305 which absorb visible light. Alternatively, a structure in which alayer formed of a silicon oxide film or the like is provided over thefirst electrode 302 so as to control a portion where recombination ofcarriers is performed may be employed.

Alternatively, a structure in which layers are stacked in the orderopposite to that of FIG. 3 and light emission is extracted to externalfrom the side opposite to the substrate may be employed. A lightemitting element shown in FIG. 4 has a structure in which the thirdlayer 305 that is an N-type semiconductor layer, the second layer 304that is a P-type semiconductor layer, the first layer 303 that is alayer containing a light emitting substance, and the first electrode 302that functions as a cathode are stacked in this order over the secondelectrode 306 that functions as an anode. In the case where thestructure shown in FIG. 4 is employed, light emission from the firstlayer 303 is extracted to external from the first electrode side whichis opposite to the substrate 301.

Furthermore, as shown in FIG. 9, a fourth layer 307 may be providedbetween the second layer 304 and the third layer 305. Through provisionof the fourth layer 307, the driving voltage can be lowered. As amaterial for forming the fourth layer 307, a semiconductor material or aconductive material may be used. As the conductive material, forexample, indium tin oxide (ITO), indium tin oxide containing silicon orsilicon oxide, indium zinc oxide (IZO), indium oxide containing tungstenoxide and zinc oxide (IWZO), or the like can be given. In addition, forexample, a film of a metal such as aluminum (Al) or silver (Ag) that isformed to have a thickness of 1 to 50 nm, preferably approximately 5 to20 nm, so as to have a light-transmitting property may be used. Inaddition, as the semiconductor material, titanium oxide (TiO_(x)),vanadium oxide (VO_(x)), niobium oxide (NbO_(x)), molybdenum oxide(MoO_(x)), tungsten oxide (WO_(x)), rhenium oxide (ReO_(x)), rutheniumoxide (RuO_(x)), cobalt oxide (CoO_(x)), nickel oxide (NiO_(x)), zincoxide (ZnO_(x)), copper oxide (CuO_(x)), tin oxide (SnO_(x)), zincsulfide (ZnS), gallium nitride (GaN), gallium aluminum nitride (AlGalN),or the like is given.

A light emitting element of the present invention has the second layer304 and the third layer 305 which absorb visible light between the lightemitting layer and the second electrode. Accordingly, light reflected bythe second electrode can be reduced and the contrast can be improved.

Furthermore, optical design of the light emitting element of the presentinvention can be performed without considering light reflected by thesecond electrode, which means that the optical design can be performedmore easily.

Furthermore, the P-type semiconductor layer and the N-type semiconductorlayer used for the light emitting element of the present invention canbe formed by vacuum evaporation. When a layer containing a lightemitting substance is formed by vacuum evaporation, any of the layerscan be formed in the same vacuum device, and the light emitting elementcan be formed in a consistent vacuum. Accordingly, attachment of aminute foreign object in the manufacturing process can be prevented anda yield can be improved.

This embodiment mode can be appropriately combined with other embodimentmodes.

(Embodiment Mode 4)

In this embodiment mode, a light emitting device including a lightemitting element of the present invention will be described.

In this embodiment mode, a light emitting device including a lightemitting element of the present invention in the pixel portion will bedescribed with reference to FIGS. 5A and 5B. FIG. 5A is a top viewshowing a light emitting device, and FIG. 5B is a cross-sectional viewalong a line A-A′ and a line B-B′ of FIG. 5A. Reference numeral 601denotes a driver circuit portion (source driver circuit), 602 denotes apixel portion, and 603 denotes a driver circuit portion (gate drivercircuit), each of which is shown by a dotted line. Reference numeral 604denotes a sealing substrate, 605 denotes a sealing member, and 607denotes a space surrounded by the sealing member 605.

A lead wire 608 is a wire for transmitting signals to be input to thesource driver circuit 601 and the gate driver circuit 603, and receivesa video signal, a clock signal, a start signal, a reset signal, and thelike from an FPC (Flexible Printed Circuit) 609 that is an externalinput terminal. Although only the FPC is shown here, a printed wiringboard (PWB) may be attached to the FPC. The light emitting device inthis specification includes not only the light emitting device itself,but also a state where the FPC or the PWB is attached to the lightemitting device.

Next, a cross-sectional structure will be described with reference toFIG. 5B. Although the driver circuit portions and the pixel portion areformed over an element substrate 610, FIG. 5B shows the source drivercircuit 601 that is the driver circuit portion and one pixel in thepixel portion 602.

The source driver circuit 601 includes a CMOS circuit formed bycombining an N-channel TFT 623 and a P-channel TFT 624. Alternatively,the driver circuit may be formed using a CMOS circuit, a PMOS circuit,or an NMOS circuit. In this embodiment mode, the integrated drivercircuit that is formed over the substrate is shown; however, the drivercircuit is not necessarily formed over the substrate and may be formedoutside the substrate.

The pixel portion 602 includes a plurality of pixels each having aswitching TFT 611, a current controlling TFT 612, and a first electrode613 that is electrically connected to a drain of the current controllingTFT 612. An insulator 614 is formed to cover an edge portion of thefirst electrode 613. In this embodiment mode, the insulator 614 isformed of a positive photosensitive acrylic resin film.

In order to improve coverage, an upper edge portion or a lower edgeportion of the insulator 614 is formed so as to have a curved surfacewith curvature. For example, if positive photosensitive acrylic is usedfor the insulator 614, it is preferable that only the upper edge portionof the insulator 614 have a curved surface with a radius of curvature of0.2 to 3 μm. Either a negative type which becomes insoluble in anetchant by light irradiation or a positive type which becomes soluble inan etchant by light irradiation can be used as the insulator 614.

A layer 616 containing a light emitting substance and a second electrode617 are formed over the first electrode 613. The first electrode 613 canbe made of various metals, an alloy, a conductive compound, or a mixturemetal, compound, or alloy thereof. If the first electrode is used as ananode, it is preferable to use, among those materials, a metal, analloy, a conductive compound, a mixture thereof, or the like with a highwork function (work function of 4.0 eV or higher), or the like. Forexample, it is possible to use a single layer film of indium tin oxidecontaining silicon, indium zinc oxide, a titanium nitride film, achromium film, a tungsten film, a Zn film, a Pt film, or the like. It isalso possible to use a stacked layer structure of a film containingtitanium nitride and a film mainly containing aluminum; a three-layerstructure of a titanium nitride film, a film mainly containing aluminum,and a titanium nitride film; or the like. The stacked layer structureachieves to have a low wire resistance, favorable ohmic contact, and afunction as an anode.

The layer 616 containing a light emitting substance is formed by variousmethods such as an evaporation method using an evaporation mask, anink-jet method, and a spin coat method. The layer 616 containing a lightemitting substance includes the layer that absorbs visible light and thelight emitting layer shown in Embodiment Mode 1. As another materialthat constitutes the layer 616 containing a light emitting substance, alow-molecular compound or a high-molecular compound (such as oligomer,dendrimer, or polymer) may be used. As the material for the layercontaining a light emitting substance, not only an organic compound butalso an inorganic compound may be used.

As a material used for the second electrode 617, various metals, analloy, a conductive compound, or a mixed metal, compound, or alloythereof may be used. In the case where the second electrode is used as acathode, a metal, an alloy, a conductive compound, a mixture thereof, orthe like with a low work function (a work function of 3.8 eV or lower)is preferably used, among others. For example, an element that belongsto Group 1 or 2 of the periodic table, that is, an alkali metal such aslithium (Li) or cesium (Cs), an alkaline earth metal such as magnesium(Mg), calcium (Ca), or strontium (Sr), an alloy containing these (Mg:Ag,Al:Li), or the like can be given. If light generated in the layer 616containing a light emitting substance is transmitted through the secondelectrode 617, the second electrode 617 can be formed using a stackedlayer structure of a metal thin film and a transparent conductive film(indium tin oxide (ITO), indium tin oxide containing silicon or siliconoxide, indium zinc oxide (IZO), indium oxide containing tungsten oxideand zinc oxide (IWZO), or the like).

When the sealing substrate 604 and the element substrate 610 areattached to each other with the sealing member 605, the light emittingelement 618 is provided in the space 607 surrounded by the elementsubstrate 610, the sealing substrate 604, and the sealing member 605.The space 607 may be filled with filler, and may be filled with an inertgas (such as nitrogen and argon), the sealing member 605, or the like.

An epoxy-based resin is preferably used for the sealing member 605. Thematerial preferably allows as little moisture and oxygen as possible topenetrate. As a material for the sealing substrate 604, a plasticsubstrate made of FRP (Fiberglass-Reinforced Plastics), PVF (polyvinylfluoride), Mylar, polyester, acrylic, or the like can be used besides aglass substrate or a quartz substrate.

In this manner, the light emitting device including the light emittingelement of the present invention can be obtained.

The light emitting device of the present invention has the layer thatabsorbs visible light described in Embodiment Mode 1. Accordingly, lightreflected by an electrode can be reduced and the contrast can beimproved.

Furthermore, optical design of the light emitting device of the presentinvention can be performed without considering light reflected by thesecond electrode, which means that the optical design can be performedmore easily.

Furthermore, by using a P-type semiconductor layer to which an acceptormaterial is added and/or an N-type semiconductor layer to which a donormaterial is added, an increase of a driving voltage can be suppressedeven when the P-type semiconductor layer and/or the N-type semiconductorlayer are/is formed to be thick. Accordingly, by fowling the P-typesemiconductor layer and/or the N-type semiconductor layer to be thick,short-circuiting caused by a minute foreign object, an impact, or thelike can be prevented; whereby a light emitting element with a highreliability can be obtained. The film thickness between the electrodesof a general light emitting element is 100 to 150 nm, however, in thecase of a light emitting element using the P-type semiconductor layerand the N-type semiconductor layer, it can be 100 to 500 nm, preferably,200 to 500 nm thick, for example.

In addition, a P-type semiconductor layer to which an acceptor materialis added and an N-type semiconductor layer to which a donor material isadded have small contact resistance with respect to electrodes. For thisreason, the electrode materials can be selected without consideringtheir work functions or the like; therefore, options of the electrodematerials are increased.

Furthermore, the light emitting device of the present invention canimprove the contrast without using a polarizing plate, a quarter-waveplate, or the like outside of the light emitting element. For thisreason, the contrast can be improved without an increase in the numberof manufacturing steps. In addition, since the polarizing plate or thequarter-wave plate is not necessarily used, a light emitting elementwith a high contrast can be manufactured at low costs.

As the above, an active light emitting device in which the drive of alight emitting element is controlled by a transistor is described inthis embodiment mode. However, the present invention may also be apassive light emitting device in which a light emitting element isdriven without a driving element such as a transistor. FIG. 6 shows aperspective view of a passive light emitting device that is manufacturedby applying the present invention. In FIG. 6, a layer 955 containing alight emitting substance is provided between an electrode 952 and anelectrode 956 over a substrate 951. An edge portion of the electrode 952is covered with an insulating layer 953. In addition, a partition layer954 is provided over the insulating layer 953. Sidewalls of thepartition layer 954 are inclined such that a distance between onesidewall and the other sidewall becomes narrower as the sidewalls getscloser to the substrate surface. In other words, a cross section of thepartition layer 954 in a direction of short side is trapezoidal shape ofwhich the lower base (the side facing in the same direction as the planedirection of the insulating layer 953 and being in contact with theinsulating layer 953) is shorter than the upper base (the side facing inthe same direction as the plane direction of the insulating layer 953and not being in contact with the insulating layer 953). In this way,with the provision of the partition layer 954, defects of the lightemitting element caused by a static electricity or the like can beprevented. Furthermore, even a passive light emitting device can achievea high contrast when it includes the light emitting element of thepresent invention with a high contrast.

(Embodiment Mode 5)

In this embodiment mode, an electronic device of the present inventionwhich includes the light emitting device described in Embodiment Mode 4in a portion thereof will be described. The electronic device of thepresent invention has a display portion excellent in contrast whichincludes the layer that absorbs visible light described in EmbodimentMode 1. In addition, it is also possible to provide an electronic devicehaving a display portion with high reliability in which short-circuitingcaused by a minute foreign object, an impact from an external source, orthe like is suppressed by making the layer that absorbs visible lightdescribed in Embodiment Mode 1 to be thick.

Examples of the electronic device manufactured by using the lightemitting device of the present invention are as follows: a camera suchas a video camera or a digital camera, a goggle type display, anavigation system, a sound reproducing device (a car audio system, anaudio component, or the like), a computer, a game machine, a portableinformation terminal (a mobile computer, a cellular phone, a mobile gamemachine, an electronic book, or the like), an image reproducing devicehaving a recording medium (specifically, a device for reproducing arecording medium such as a digital versatile disc (DVD) and having adisplay for displaying the image), and the like. Specific examples ofthese electronic devices are shown in FIGS. 7A to 7D.

FIG. 7A shows a television device according to the present invention,which includes a chassis 9101, a support base 9102, a display portion9103, a speaker portion 9104, a video input terminal 9105, and the like.In this television device, the display portion 9103 includes lightemitting elements similar to those described in Embodiment Modes 2 and3, which are arranged in a matrix. The light emitting element isexcellent in contrast. In addition, short-circuiting caused by a minuteforeign object, an impact from an external source, or the like can beprevented. The display portion 9103 which includes the light emittingelement also has a similar feature. Accordingly, the television devicecan realize a high contrast and display a high-quality image. Inaddition, the television device of the present invention can realize ahigh contrast even when the number of its components is smaller than theconventional case; therefore it can be manufactured at low costs.Furthermore, when the number of components is reduced, reductions insize and weight of the chassis 9101 can be achieved. Since animprovement in image quality and reductions in size and weight areachieved in the television device of the present invention, a productwhich is suitable for the living environment can be provided.

FIG. 7B shows a computer according to the present invention, whichincludes a main body 9201, a chassis 9202, a display portion 9203, akeyboard 9204, an external connection port 9205, a pointing mouse 9206,and the like. In this computer, the display portion 9203 includes lightemitting elements similar to those described in Embodiment Modes 2 and3, which are arranged in a matrix. The light emitting element isexcellent in contrast. In addition, short-circuiting caused by a minuteforeign object, an impact from an external source, or the like can beprevented. The display portion 9203 which includes the light emittingelement also has a similar feature. Accordingly, the computer canrealize a high contrast and display a high-quality image. In addition,the computer of the present invention can realize a high contrast evenwhen the number of its components is smaller than the conventional case;therefore it can be manufactured at low costs. Furthermore, when thenumber of components is reduced, reductions in size and weight of thechassis 9202 can be achieved. Since an improvement in image quality andreductions in size and weight are achieved in the computer of thepresent invention, a product which is suitable for the environment canbe provided. In addition, a portable computer can be provided.

FIG. 7C shows a cellular phone according to the present invention, whichincludes a main body 9401, a chassis 9402, a display portion 9403, anaudio input portion 9404, an audio output portion 9405, an operation key9406, an external connection port 9407, an antenna 9408, and the like.In this cellular phone, the display portion 9403 includes light emittingelements similar to those described in Embodiment Modes 2 and 3, whichare arranged in a matrix. The light emitting element is excellent incontrast. In addition, short-circuiting caused by a minute foreignobject, an impact from an external source, or the like can be prevented.The display portion 9403 which includes the light emitting element alsohas a similar feature. Accordingly, the cellular phone can realize ahigh contrast and display a high-quality image. In addition, thecellular phone of the present invention can realize a high contrast evenwhen the number of its components is smaller than the conventional case;therefore it can be manufactured at low costs. Furthermore, when thenumber of components is reduced, reductions in size and weight of thechassis 9402 can be achieved. Since an improvement in image quality andreductions in size and weight are achieved in the cellular phone of thepresent invention, a product which is suitable for being carried can beprovided. In addition, a product including a display portion resistantto an impact from an external source when being carried can be provided.

FIG. 7D shows a camera according to the present invention, whichincludes a main body 9501, a display portion 9502, a chassis 9503, anexternal connection port 9504, a remote control receiving portion 9505,an image receiving portion 9506, a battery 9507, an audio input portion9508, operation keys 9509, an eye piece portion 9510, and the like. Inthis camera, the display portion 9502 includes light emitting elementssimilar to those described in Embodiment Modes 2 and 3, which arearranged in a matrix. The light emitting element is excellent incontrast. In addition, short-circuiting caused by a minute foreignobject, an impact from an external source, or the like can be prevented.The display portion 9502 which includes the light emitting element alsohas a similar feature. Accordingly, the camera can realize a highcontrast and display a high-quality image. In addition, the camera ofthe present invention can realize a high contrast even when the numberof its components is smaller than the conventional case; therefore itcan be manufactured at low costs. Furthermore, when the number ofcomponents is reduced, reductions in size and weight of the chassis 9503can be achieved. Since an improvement in image quality and reductions insize and weight are achieved in the camera of the present invention, aproduct which is suitable for being carried can be provided. Inaddition, a product including a display portion resistant to an impactfrom an external source when being carried can be provided.

As described above, the applicable range of the light emitting device ofthe present invention is so wide that the light emitting device can beapplied to electronic devices of various fields. By using the lightemitting device of the present invention, an electronic device includinga display portion with a high contrast can be provided.

[Embodiment 1]

In this embodiment, a light emitting element of the present inventionwill be specifically described with reference to FIG. 10. Structuralformulas of organic compounds used in this embodiment are shown below.It is to be noted that all the light emitting elements manufactured inthis embodiment are manufactured over the same substrate.

(Light Emitting Element 1)

First, a film of indium tin oxide containing silicon oxide was formedover a glass substrate 510 by a sputtering method; whereby a firstelectrode 511 was formed. The thickness was 110 nm and the electrodearea was 2 mm×2 mm.

Next, the substrate on which the first electrode 511 was formed wasfixed to a substrate holder that was provided in a vacuum evaporationapparatus, such that the surface on which the first electrode 511 wasformed came to the lower side. After the pressure was reduced to beapproximately 10⁻⁴ Pa,4,4′-bis(N-{4-[N′-(3-methylphenyl)-N′-phenylamino]phenyl}-N-phenylamino)biphenyl(abbreviation: DNTPD) and molybdenum oxide (VI) were co-evaporated onthe first electrode 511; whereby a layer 512 containing a compositematerial was formed. The thickness was 50 nm, and the weight ratio ofDNTPD to molybdenum oxide (VI) was adjusted so as to be 1:0.5 (=DNTPD:molybdenum oxide). It is to be noted that a co-evaporation method is amethod in which evaporations from a plurality of evaporation sources areperformed at the same time in one treatment chamber.

Next, 4,4′-bis[N-(1-naphthyl)-N-phenylamino]biphenyl (abbreviation: NPB)was formed to have a thickness of 10 nm by an evaporation method usingresistance heating; whereby a hole-transporting layer 513 was formed.

Furthermore, a light emitting layer 514 with a thickness of 40 nm wasformed on the hole-transporting layer 513 by co-evaporatingtris(8-quinolinolato)aluminum (abbreviation: Alq) and coumarin 6. Theweight ratio of Alq to coumarin 6 was adjusted so as to be 1:0.01 (=Alq:coumarin 6).

After that, a film of Alq was formed to have a thickness of 10 nm on thelight emitting layer 514, by an evaporation method using resistanceheating; whereby an electron-transporting layer 515 was tot med.

An electron-injecting layer 516 with a thickness of 10 nm was formed onthe electron-transporting layer 515 by co-evaporating Alq and lithium(Li). The weight ratio of Alq to lithium was adjusted so as to be 1:0.01(=Mg: lithium).

An N-type semiconductor layer 517 with a thickness of 70 nm was formedon the electron-injecting layer 516 by co-evaporating3,4,9,10-perylenetetracarboxylicdianhydride (abbreviation: PTCDA) andlithium. The weight ratio of PTCDA to lithium was adjusted so as to be1:0.01 (=PTCDA: lithium).

Furthermore, a P-type semiconductor layer 518 with a thickness of 80 nmwas formed by co-evaporating copper phthalocyanine (abbreviation: CuPc)and molybdenum oxide (VI). The weight ratio of CuPc to molybdenum oxidewas adjusted so as to be 1:0.5 (=CuPc: molybdenum oxide).

Finally, a film of aluminum was formed to have a thickness of 200 nm byan evaporation method using resistance heating; whereby a secondelectrode 519 was formed. In this manner, a light emitting element 1 wasmanufactured.

(Comparative Light Emitting Element 2)

First, a film of indium tin oxide containing silicon oxide was formedover a glass substrate by a sputtering method; whereby a first electrodewas formed. The thickness was 110 nm and the electrode area was 2 mm×2mm.

Next, the substrate on which the first electrode was formed was fixed toa substrate holder that was provided in a vacuum evaporation apparatus,such that the surface on which the first electrode was formed came tothe lower side. After the pressure was reduced to be approximately 10⁻⁴Pa,4,4′-bis(N-{4-[N′-(3-methylphenyl)-N-phenylamino]phenyl}-N-phenylamino)biphenyl(abbreviation: DNTPD) and molybdenum oxide (VI) were co-evaporated onthe first electrode; whereby a layer containing a composite material wasformed. The thickness was 50 nm, and the weight ratio of DNTPD tomolybdenum oxide (VI) was adjusted so as to be 1:0.5 (=DNTPD: molybdenumoxide). It is to be noted that a co-evaporation method is a method inwhich evaporations from a plurality of evaporation sources are performedat the same time in one treatment chamber.

Next, 4,4′-bis[N-(1-naphthyl)-N-phenylamino]biphenyl (abbreviation: NPB)was formed to have a thickness of 10 nm by an evaporation method usingresistance heating; whereby a hole-transporting layer was formed.

Furthermore, a light emitting layer with a thickness of 40 nm was formedon the hole-transporting layer by co-evaporatingtris(8-quinolinolato)aluminum (abbreviation: Alq) and coumarin 6. Theweight ratio of Alq to coumarin 6 was adjusted so as to be 1:0.01 (=Alq:coumarin 6).

After that, a film of Alq was formed to have a thickness of 10 nm on thelight emitting layer, by an evaporation method using resistance heating;whereby an electron-transporting layer was formed.

An electron-injecting layer with a thickness of 20 nm was formed overthe electron-transporting layer by co-evaporating Alq and lithium (Li).The weight ratio of Alq to lithium was adjusted so as to be 1:0.01(=Alq: lithium).

Finally, a film of aluminum was formed to have a thickness of 200 nm byan evaporation method using resistance heating; whereby a secondelectrode was formed. In this manner, a comparative light emittingelement 2 was manufactured.

(Comparative Light Emitting Element 3)

First, a film of indium tin oxide containing silicon oxide was formedover a glass substrate by a sputtering method; whereby a first electrodewas formed. The thickness was 110 nm and the electrode area was 2 mm×2mm.

Next, the substrate on which the first electrode was formed was fixed toa substrate holder that was provided in a vacuum evaporation apparatus,such that the surface on which the first electrode was formed came tothe lower side. After the pressure was reduced to be approximately 10⁻⁴Pa,4,4′-bis(N-{4-[N′-(3-methylphenyl)-N′-phenylamino]phenyl}-N-phenylamino)biphenyl(abbreviation: DNTPD) and molybdenum oxide (VI) were co-evaporated onthe first electrode; whereby a layer containing a composite material wasformed. The thickness was 50 nm, and the weight ratio of DNTPD tomolybdenum oxide (VI) was adjusted so as to be 1:0.5 (=DNTPD: molybdenumoxide). It is to be noted that a co-evaporation method is a method inwhich evaporations from a plurality of evaporation sources are performedat the same time in one treatment chamber.

Next, 4,4′-bis[N-(1-naphthyl)-N-phenylamino]biphenyl (abbreviation: NPB)was formed to have a thickness of 10 nm by an evaporation method usingresistance heating; whereby a hole-transporting layer was formed.

Furthermore, a light emitting layer with a thickness of 40 nm was formedon the hole-transporting layer by co-evaporatingtris(8-quinolinolato)aluminum (abbreviation: Alq) and coumarin 6. Theweight ratio of Alq to coumarin 6 was adjusted so as to be 1:0.01 (=Alq:coumarin 6).

After that, a film of Alq was formed to have a thickness of 10 nm on thelight emitting layer, by an evaporation method using resistance heating;whereby an electron-transporting layer was formed.

An electron-injecting layer with a thickness of 10 nm was formed on theelectron-transporting layer by co-evaporating Alq and lithium (Li). Theweight ratio of Alq to lithium was adjusted so as to be 1:0.01 (=Alq:lithium).

A layer with a thickness of 150 nm was formed on the electron-injectinglayer by co-evaporating 3,4,9,10-perylenetetracarboxylicdianhydride(abbreviation: PTCDA) and lithium. The weight ratio of PTCDA to lithiumwas adjusted so as to be 1:0.01 (═PTCDA: lithium).

Finally, a film of aluminum was formed to have a thickness of 200 nm byan evaporation method using resistance heating; whereby a secondelectrode was Mimed. In this manner, a comparative light emittingelement 3 was manufactured.

(Comparative Light Emitting Element 4)

First, a film of indium tin oxide containing silicon oxide was formedover a glass substrate by a sputtering method; whereby a first electrodewas formed. The thickness was 110 nm and the electrode area was 2 mm×2mm.

Next, the substrate on which the first electrode was formed was fixed toa substrate holder that was provided in a vacuum evaporation apparatus,such that the surface on which the first electrode was formed came tothe lower side. After the pressure was reduced to be approximately 10⁻⁴Pa,4,4′-bis(N-{4-[N′-(3-methylphenyl)-N-phenylamino]phenyl}-N-phenylamino)biphenyl(abbreviation: DNTPD) and molybdenum oxide (VI) were co-evaporated onthe first electrode; whereby a layer containing a composite material wasformed. The thickness was 50 nm, and the weight ratio of DNTPD tomolybdenum oxide (VI) was adjusted so as to be 1:0.5 (=DNTPD: molybdenumoxide). It is to be noted that a co-evaporation method is a method inwhich evaporations from a plurality of evaporation sources are performedat the same time in one treatment chamber.

Next, 4,4′-bis[N-(1-naphthyl)-N-phenylamino]biphenyl (abbreviation: NPB)was formed to have a thickness of 10 nm by an evaporation method usingresistance heating; whereby a hole-transporting layer was formed.

Furthermore, a light emitting layer with a thickness of 40 nm was formedon the hole-transporting layer by co-evaporatingtris(8-quinolinolato)aluminum (abbreviation: Alq) and coumarin 6. Theweight ratio of Alq to coumarin 6 was adjusted so as to be 1:0.01 (=Alq:coumarin 6).

After that, a film of Alq was formed to have a thickness of 10 nm on thelight emitting layer, by an evaporation method using resistance heating;whereby an electron-transporting layer was formed.

An electron-injecting layer with a thickness of 20 nm was formed on theelectron-transporting layer by co-evaporating Alq and lithium (Li). Theweight ratio of Alq to lithium was adjusted so as to be 1:0.01 (=Alq:lithium).

Furthermore, a layer with a thickness of 140 nm was formed byco-evaporating DNTPD and molybdenum oxide (VI). The weight ratio ofDNTPD to molybdenum oxide was adjusted so as to be 1:0.5 (=DNTPD:molybdenum oxide).

Finally, a film of aluminum was fondled to have a thickness of 200 nm byan evaporation method using resistance heating; whereby a secondelectrode was formed. In this manner, a comparative light emittingelement 4 was manufactured.

The current efficiency-luminance characteristics of the light emittingelement 1, the comparative light emitting element 2, the comparativelight emitting element 3, and the comparative light emitting element 4are shown in FIG. 11. In addition, the current-voltage characteristicsthereof are shown in FIG. 12. Furthermore, the emission spectrumsthereof are shown in FIG. 13. It can be seen from FIG. 11 that thecurrent efficiency of the light emitting element 1 and the comparativelight emitting element 3 is almost half compared to that of thecomparative light emitting element 2 and the comparative light emittingelement 4. This means that the layer formed on the second electrode sideof the light emitting layer absorbs light emitted from the lightemitting layer in each of the light emitting element 1 and thecomparative light emitting element 3.

In FIG. 14, absorption spectrums of PTCDA, CuPc, and DNTPD which wereused for the light emitting element 1, the comparative light emittingelement 3, or the comparative light emitting element 4 are shown. Theabsorption spectrums shown in FIG. 14 were obtained by measuring thesamples of PTCDA, CuPc, and DNTPD each formed with a thickness of 50 nmover a quartz substrate by an evaporation method. As shown in FIG. 14,PTCDA and CuPc which were used for the light emitting element 1 haveabsorption peaks in different regions from each other in the visiblelight region. Specifically, PTCDA has the absorption peaks at 485 um and559 nm, and CuPc has the absorption peaks at 624 nm and 695 nm.Furthermore, it can be seen from FIG. 14 that DNTPD does not have anabsorption peak in the visible light region.

In addition, the contrast ratios of the light emitting element 1, thecomparative light emitting element 2, and the comparative light emittingelement 3 were measured under the illumination of 100 (1×). The resultswere, when the contrast of the comparative light emitting element 2 wasto be 1, the contrast ratios of the comparative light emitting element 3and the light emitting element 1 were 26 and 78, respectively. It wasfound that the light emitting element to which the present invention wasapplied had a higher contrast ratio than those of the comparative lightemitting element 2 and the comparative light emitting element 3. Forthis reason, a light emitting element with a high contrast ratio can beobtained by applying the present invention.

The comparative light emitting element 2 is a light emitting elementwhich has a structure generally manufactured. Although the currentefficiency thereof is high, the contrast ratio is low. The comparativelight emitting element 4 has a structure in which the layer containingDNTPD is provided between the light emitting layer and the secondelectrode. The layer containing DNTPD transmits a large part of visiblelight; therefore, it is assumed that the current efficiency is high andthe contrast is low, similarly to the comparative light emitting element2.

On the other hand, the comparative light emitting element 3 uses a layercontaining PTCDA, and can partially absorb visible light. In particular,since light emission of coumarin 6 which is used for the light emittinglayer of the light emitting element of this embodiment has the spectrumas shown in FIG. 13, light emitted from the light emitting layer (greenlight) can be absorbed by the layer containing PTCDA. Accordingly, thecurrent efficiency is low as shown in FIG. 11. However, it is impossibleto absorb visible light over a wide wavelength range; therefore, part oflight from an external source is reflected by the second electrode.Accordingly, the contrast of the comparative light emitting element 3 islower than that of the light emitting element 1.

On the other hand, the light emitting element 1 can absorb light emittedfrom the light emitting layer and incident light from an external sourceover the whole visible light region by the N-type semiconductor layercontaining PTCDA and the P-type semiconductor layer containing CuPc.Accordingly, a high contrast can be realized.

Furthermore, it can be seen from FIG. 13 that light emitted from thelight emitting layer of the comparative light emitting elementinterferes with light reflected by the second electrode and the emissionspectrum is changed. Specifically, peaks of the emission spectrums ofthe comparative light emitting element 2, the comparative light emittingelement 3, and the comparative light emitting element 4 are broader thanthat of the light emitting element 1. In other words, the shapes of theemission spectrums are changed by interference effect caused by thesecond electrode. On the other hand, the light emitting element 1 cansuppress light reflected by the second electrode; therefore, the opticaldesign can be performed without considering the interference effect. Inaddition, since the interference from reflected light is suppressed, theshape of the emission spectrum is not changed and light emission withhigh color purity can be obtained.

Furthermore, it can be seen from FIG. 12 that the current-voltagecharacteristics of the light emitting element 1, the comparative lightemitting element 2, the comparative light emitting element 3, and thecomparative light emitting element 4 are not much different. Thethickness of the layers containing a light emitting substance interposedbetween electrodes in the light emitting element 1 is 140 nm thicker asa whole than that in the comparative light emitting element 2. In spiteof this, the current-voltage characteristic of the light emittingelement 1 is not much different from that of the comparative lightemitting element 2. Accordingly, an increase in driving voltage can besuppressed even when the P-type semiconductor layer and the N-typesemiconductor layer are made thick.

[Embodiment 2]

In this embodiment, a light emitting element of the present inventionwill be described with reference to FIG. 10. Structural formulas oforganic compounds used in this embodiment are shown below. It is to benoted that a light emitting element 5 and a comparative light emittingelement 6 are manufactured over the same substrate.

(Light Emitting Element 5)

First, a film of indium tin oxide containing silicon oxide was formedover a glass substrate 510 by a sputtering method; whereby a firstelectrode 511 was formed. The thickness was 110 nm and the electrodearea was 2 mm×2 mm.

Next, the substrate on which the first electrode 511 was foamed wasfixed to a substrate holder that was provided in a vacuum evaporationapparatus, such that the surface on which the first electrode 511 wasformed came to the lower side. After the pressure was reduced to beapproximately 10⁻⁴ Pa,4,4′-bis(N-{4-[N′-(3-methylphenyl)-N′-phenylamino]phenyl}-N-phenylamino)biphenyl(abbreviation: DNTPD) and molybdenum oxide (VI) were co-evaporated onthe first electrode 511; whereby a layer 512 containing a compositematerial was formed. The thickness was 50 nm, and the weight ratio ofDNTPD to molybdenum oxide (VI) was adjusted so as to be 1:0.5 (=DNTPD:molybdenum oxide). It is to be noted that a co-evaporation method is amethod in which evaporations from a plurality of evaporation sources areperformed at the same time in one treatment chamber.

Next, 4,4′-bis[N-(1-naphthyl)-N-phenylamino]biphenyl (abbreviation: NPB)was formed to have a thickness of 10 nm by an evaporation method usingresistance heating; whereby a hole-transporting layer 513 was formed.

Furthermore, a light emitting layer 514 with a thickness of 40 nm wasformed on the hole-transporting layer 513 by co-evaporatingtris(8-quinolinolato)aluminum (abbreviation: Alq) and coumarin 6. Theweight ratio of Alq to coumarin 6 was adjusted so as to be 1:0.01 (=Alq:coumarin 6).

After that, a film of Alq was formed to have a thickness of 10 nm on thelight emitting layer 514, by an evaporation method using resistanceheating; whereby an electron-transporting layer 515 was formed.

An electron-injecting layer 516 with a thickness of 10 nm was formed onthe electron-transporting layer 515 by co-evaporating Alq and lithium(Li). The weight ratio of Alq to lithium was adjusted so as to be 1:0.01(=Alq: lithium).

An N-type semiconductor layer 517 with a thickness of 60 nm was formedon the electron-injecting layer 516 by co-evaporating3,4,9,10-perylenetetracarboxylic-bis-benzimidazole (abbreviation:PTCBI), and lithium. The weight ratio of PTCBI to lithium was adjustedso as to be 1:0.01 (=PTCBI: lithium).

Furthermore, a P-type semiconductor layer 518 with a thickness of 90 nmwas formed by co-evaporating rubrene and molybdenum oxide (VI). Theweight ratio of rubrene to molybdenum oxide was adjusted so as to be1:0.5 (=rubrene: molybdenum oxide).

Finally, a film of aluminum was formed to have a thickness of 200 nm byan evaporation method using resistance heating; whereby a secondelectrode 519 was formed. In this manner, a light emitting element 5 wasmanufactured.

(Comparative Light Emitting Element 6)

First, a film of indium tin oxide containing silicon oxide was formedover a glass substrate by a sputtering method; whereby a first electrodewas formed. The thickness was 110 nm and the electrode area was 2 mm×2mm.

Next, the substrate on which the first electrode was formed was fixed toa substrate holder that was provided in a vacuum evaporation apparatus,such that the surface on which the first electrode was formed came tothe lower side. After the pressure was reduced to be approximately 10⁻⁴Pa,4,4′-bis(N-{4-[N′-(3-methylphenyl)-N′-phenylamino]phenyl}-N-phenylamino)biphenyl(abbreviation: DNTPD) and molybdenum oxide (VI) were co-evaporated onthe first electrode; whereby a layer containing a composite material wasformed. The thickness was 50 nm, and the weight ratio of DNTPD tomolybdenum oxide (VI) was adjusted so as to be 1:0.5 (=DNTPD: molybdenumoxide). It is to be noted that a co-evaporation method is a method inwhich evaporations from a plurality of evaporation sources are performedat the same time in one treatment chamber.

Next, 4,4′-bis[N-(1-naphthyl)-N-phenylamino]biphenyl (abbreviation: NPB)was formed to have a thickness of 10 nm by an evaporation method usingresistance heating; whereby a hole-transporting layer was fanned.

Furthermore, a light emitting layer with a thickness of 40 nm was formedon the hole-transporting layer by co-evaporatingtris(8-quinolinolato)aluminum (abbreviation: Alq) and coumarin 6. Theweight ratio of Alq to coumarin 6 was adjusted so as to be 1:0.01 (=Alq:coumarin 6).

After that, a film of Alq was formed to have a thickness of 10 nm on thelight emitting layer, by an evaporation method using resistance heating;whereby an electron-transporting layer was formed.

An electron-injecting layer with a thickness of 20 nm was formed on theelectron-transporting layer by co-evaporating Alq and lithium (Li). Theweight ratio of Alq to lithium was adjusted so as to be 1:0.01 (=Alq:lithium).

Finally, a film of aluminum was formed to have a thickness of 200 nm byan evaporation method using resistance heating; whereby a secondelectrode was formed. In this manner, a comparative light emittingelement 6 was manufactured.

The current efficiency-luminance characteristics of the light emittingelement 5 and the comparative light emitting element 6 are shown in FIG.15. In addition, the current-voltage characteristics thereof are shownin FIG. 16. Furthermore, the emission spectrums thereof are shown inFIG. 17. It can be seen from FIG. 15 that the current efficiency of thelight emitting element 5 is almost half compared to that of thecomparative light emitting element 6. This means that the layer formedon the second electrode side of the light emitting layer absorbs lightemitted from the light emitting layer in the light emitting element 5.

In FIG. 18, absorption spectrums of PTCBI and rubrene which were usedfor the light emitting element 5 are shown. The absorption spectrumsshown in FIG. 18 were obtained by measuring the samples of PTCBI andrubrene each formed over a quartz substrate by an evaporation method. Asshown in FIG. 18, PTCBI and rubrene which were used for the lightemitting element 5 have the absorption peaks in different regions fromeach other in the visible light region. Specifically, PTCBI has theabsorption peak at 548 nm, and rubrene has the absorption peaks at 496nm and 531 nm.

In addition, the contrast ratios of the light emitting element 5 and thecomparative light emitting element 6 were measured under theillumination of 100 (1×). The results were, when the contrast of thecomparative light emitting element 6 was set to be 1, the contrast ratioof the light emitting element 5 was 17. It was found that the lightemitting element to which the present invention was applied had a highercontrast ratio than that of the comparative light emitting element 6.For this reason, a light emitting element with a high contrast ratio canbe obtained by applying the present invention.

The comparative light emitting element 6 is a light emitting elementwhich has a structure generally manufactured, in which the currentefficiency is high but the contrast is low.

On the other hand, the light emitting element 5 can absorb light emittedfrom the light emitting layer and incident light from an external sourceover the whole visible light region by the N-type semiconductor layercontaining PTCBI and the P-type semiconductor layer containing rubrene.Accordingly, a high contrast can be realized.

Furthermore, it can be seen from FIG. 17 that light emitted from thelight emitting layer of the comparative light emitting elementinterferes with light reflected by the second electrode and the emissionspectrum is changed. Specifically, a peak of the emission spectrum ofthe comparative light emitting element 6 is broader than that of thelight emitting element 5. In other words, the shape of the emissionspectrum is changed by interference effect caused by the secondelectrode. On the other hand, the light emitting element 5 can suppresslight reflected by the second electrode; therefore, the optical designcan be performed without considering the interference effect. Inaddition, since the interference from reflected light is suppressed, theshape of the emission spectrum is not changed and light emission withhigh color purity can be obtained.

Furthermore, it can be seen from FIG. 16 that the current-voltagecharacteristics of the light emitting element 5 and the comparativelight emitting element 6 are not much different. The thickness of thelayers containing a light emitting substance interposed betweenelectrodes in the light emitting element 5 is 140 nm thicker as a wholethan that in the comparative light emitting element 6. In spite of this,the current-voltage characteristic of the light emitting element 5 isnot much different from that of the comparative light emitting element6. Accordingly, an increase in driving voltage can be suppressed evenwhen the P-type semiconductor layer and the N-type semiconductor layerare made thick.

This application is based on Japanese Patent Application serial No.2006-061969 filed in Japan Patent Office on Mar. 8, 2006, the contentsof which are hereby incorporated by reference.

What is claimed is:
 1. A light emitting element comprising: a firstelectrode; a second electrode; and a first layer containing a lightemitting substance interposed between the first electrode and the secondelectrode, wherein the first layer comprises: a light emitting layer; asecond layer containing a first organic compound; and a third layercontaining a second organic compound, wherein the first electrode has alight-transmitting property, wherein the second layer and the thirdlayer are interposed between the second electrode and the light emittinglayer, and wherein the first organic compound has an absorption peak ina wavelength region of greater than or equal to 380 nm and less than 540nm, and the second organic compound has an absorption peak in awavelength region of greater than or equal to 540 nm and less than orequal to 760 nm.
 2. The light emitting element according to claim 1,further comprising a fourth layer between the second layer and the thirdlayer, wherein the fourth layer contains a conductive material.
 3. Thelight emitting element according to claim 2, wherein the conductivematerial is one selected from the group consisting of indium tin oxide,indium tin oxide containing silicon or silicon oxide, indium zinc oxide,and indium tin oxide containing tungsten oxide and zinc oxide.
 4. Thelight emitting element according to claim 1, further comprising a fourthlayer between the second layer and the third layer, wherein the fourthlayer contains a semiconductor material.
 5. The light emitting elementaccording to claim 4, wherein the semiconductor material is one selectedfrom the group consisting of titanium oxide, vanadium oxide, niobiumoxide, molybdenum oxide, tungsten oxide, rhenium oxide, ruthenium oxide,cobalt oxide, nickel oxide, zinc oxide, copper oxide, tin oxide, zincsulfide, gallium nitride, and gallium aluminum nitride.
 6. The lightemitting element according to claim 1, wherein the first organiccompound is any of 3,4,9,10-perylenetetracarboxylic acid derivatives,1,4,5,8,-naphthalenetetracarboxylic acid derivatives, naphthacenederivatives, or nickel complexes, and wherein the second organiccompound is any of phthalocyanine derivatives, pentacene derivatives,3,4,9,10-perylenetetracarboxylic-bis-benzimidazole derivatives, orviolanthrone derivatives.
 7. The light emitting element according toclaim 1, further comprising a fourth layer including a metal oxide,wherein a thickness of the fourth layer is 50 nm to 150 nm, wherein atotal thickness of the second layer and the third layer is 150 nm ormore, and wherein color of the first organic compound and color of thesecond organic compound are complementary colors to each other so thatat least a portion of light emitted from the light emitting layer can beabsorbed by the second layer and the third layer.
 8. A light emittingelement comprising: a first electrode; a second electrode; and a firstlayer containing a light emitting substance interposed between the firstelectrode and the second electrode, wherein the first layer comprises: alight emitting layer; a first semiconductor layer; and a secondsemiconductor layer, wherein the first electrode, the light emittinglayer, the first semiconductor layer, the second semiconductor layer,and the second electrode are formed in this order, wherein the firstelectrode has a light-transmitting property, wherein one of the firstsemiconductor layer and the second semiconductor layer is an N-typesemiconductor layer and the other one of the first semiconductor layerand the second semiconductor layer is a P-type semiconductor layer, andwherein the N-type semiconductor layer has an absorption peak in awavelength region of greater than or equal to 380 nm and less than 540nm, and the P-type semiconductor layer has an absorption peak in awavelength region of greater than or equal to 540 nm and less than orequal to 760 nm.
 9. The light emitting element according to claim 8,further comprising a second layer between the first semiconductor layerand the second semiconductor layer, wherein the second layer contains aconductive material.
 10. The light emitting element according to claim9, wherein the conductive material is one selected from the groupconsisting of indium tin oxide, indium tin oxide containing silicon orsilicon oxide, indium zinc oxide, and indium tin oxide containingtungsten oxide and zinc oxide.
 11. The light emitting element accordingto claim 8, further comprising a second layer between the firstsemiconductor layer and the second semiconductor layer, wherein thesecond layer contains a semiconductor material.
 12. The light emittingelement according to claim 11, wherein the semiconductor material is oneselected from the group consisting of titanium oxide, vanadium oxide,niobium oxide, molybdenum oxide, tungsten oxide, rhenium oxide,ruthenium oxide, cobalt oxide, nickel oxide, zinc oxide, copper oxide,tin oxide, zinc sulfide, gallium nitride, and gallium aluminum nitride.13. The light emitting element according to claim 8, wherein the P-typesemiconductor layer further contains an acceptor material.
 14. The lightemitting element according to claim 8, wherein the N-type semiconductorlayer further contains a donor material.
 15. The light emitting elementaccording to claim 8, wherein the N-type semiconductor layer containsany of 3,4,9,10-perylenetetracarboxylicdianhydride,3,4,9,10-perylenetetracarboxylicdiimide,N,N′-dimethyl-3,4,9,10-perylenetetracarboxylicdiimide,1,4,5,8-naphthalenetetracarboxylicdianhydride, or1,4,5,8-naphthalenetetracarboxylicdiimide, and wherein the P-typesemiconductor layer contains any of phthalocyanine, copperphthalocyanine, zinc phthalocyanine, vanadyl phthalocyanine, titanylphthalocyanine, nickel phthalocyanine, pentacene, or6,13-diphenylpentacene.
 16. The light emitting element according toclaim 8, further comprising a second layer including a metal oxide,wherein a thickness of the second layer is 50 nm to 150 nm, wherein atotal thickness of the first semiconductor layer and the secondsemiconductor layer is 150 nm or more, and wherein color of the firstsemiconductor layer and color of the second semiconductor layer arecomplementary colors to each other so that at least a portion of lightemitted from the light emitting layer can be absorbed by the firstsemiconductor layer and the second semiconductor layer.
 17. A lightemitting element comprising: a first electrode; a second electrode; anda first layer containing a light emitting substance interposed betweenthe first electrode and the second electrode, wherein the first layercomprises: a light emitting layer; a first semiconductor layer; and asecond semiconductor layer, wherein the first electrode, the lightemitting layer, the first semiconductor layer, the second semiconductorlayer, and the second electrode are formed in this order, wherein thefirst electrode has a light-transmitting property, wherein one of thefirst semiconductor layer and the second semiconductor layer is anN-type semiconductor layer and the other one of the first semiconductorlayer and the second semiconductor layer is a P-type semiconductorlayer, wherein the N-type semiconductor layer has an absorption peak ina wavelength region of greater than or equal to 540 nm and less than orequal to 760 nm, and wherein the P-type semiconductor layer has anabsorption peak in a wavelength region of greater than or equal to 380nm and less than 540 nm.
 18. The light emitting element according toclaim 17, further comprising a second layer between the firstsemiconductor layer and the second semiconductor layer, wherein thesecond layer contains a conductive material.
 19. The light emittingelement according to claim 18, wherein the conductive material is oneselected from the group consisting of indium tin oxide, indium tin oxidecontaining silicon or silicon oxide, indium zinc oxide, and indium tinoxide containing tungsten oxide and zinc oxide.
 20. The light emittingelement according to claim 17, further comprising a second layer betweenthe first semiconductor layer and the second semiconductor layer,wherein the second layer contains a semiconductor material.
 21. Thelight emitting element according to claim 20, wherein the semiconductormaterial is one selected from the group consisting of titanium oxide,vanadium oxide, niobium oxide, molybdenum oxide, tungsten oxide, rheniumoxide, ruthenium oxide, cobalt oxide, nickel oxide, zinc oxide, copperoxide, tin oxide, zinc sulfide, gallium nitride, and gallium aluminumnitride.
 22. The light emitting element according to claim 17, whereinthe P-type semiconductor layer further contains an acceptor material.23. The light emitting element according to claim 17, wherein the N-typesemiconductor layer further contains a donor material.
 24. The lightemitting element according to claim 17, wherein the N-type semiconductorlayer contains any of(1,2,3,4,8,9,10,11,15,16,17,18,22,23,24,25-hexadecafluorophthalocyaninato)copper,(1,2,3,4,8,9,10,11,15,16,17,18,22,23,24,25-hexadecafluorophthalocyaninato)zinc,perfluoropentacene, or3,4,9,10-perylenetetracarboxylic-bis-benzimidazole, and wherein theP-type semiconductor layer contains any of naphthacene,5,12-diphenylnaphthacene, or rubrene.
 25. The light emitting elementaccording to claim 17, further comprising a second layer including ametal oxide, wherein a thickness of the second layer is 50 nm to 150 nm,wherein a total thickness of the first semiconductor layer and thesecond semiconductor layer is 150 nm or more, and wherein color of thefirst semiconductor layer and color of the second semiconductor layerare complementary colors to each other so that at least a portion oflight emitted from the light emitting layer can be absorbed by the firstsemiconductor layer and the second semiconductor layer.